1 Introduction

Traditionally, organizations are categorized into the public, private, and third sectors (Avidar, 2017; Carswell et al., 2012; Hyde, 2023), and have long shaped our collective landscape by reflecting the cultural patterns, values and norms of the society in which they emerged. Nevertheless, globalization, the shifts of technological advancement, and the growing complexities of contemporary societies have reshaped the narrative of organizational existence (Fourth Sector Network, 2009; Pires, 2017; Rask et al., 2020).

Nowadays, society faces complex problems, dispersed on a global scale (Carswell et al., 2012; Stötzer et al., 2020) of economic, social and environmental nature, such as corruption, global warming and even a pandemic crisis (Martins et al., 2021), not to mention a large disparity between rich and poor, and traditional sectors (public, private sector, and the third sector) by themselves are not able to respond to these challenges, forcing them to work together (Guerrero & Hansen, 2018; Howlett & Lejano, 2013). Increased awareness of social and environmental issues, and the desire of individuals and organizations to address these issues in a meaningful way have led to a shift in values, as more and more people prioritize the impact of their actions on others and the planet. Given their complexity, these deep and progressive changes in society imply new ways of thinking and acting, triggering the emergence of activities that do not fit into traditional sectors and constitute new organizational configurations (Sánchez-Hernández et al., 2021a, b). At the same time, we now face a growing trend of migration to urban areas, which has led to increased demand for services and support, thus creating opportunities for organizations to address pressing social and environmental issues in urban settings. Several authors call this phenomenon the blurring of boundaries between traditional sectors (Avidar, 2017; Carswell et al., 2012; Fourth Sector Network, 2009; Sabeti, 2011).

In the public sector there has been a slimming down of the state, for sometimes we face the inability of governments to fully address social issues on their own, and other times we have smaller governments and the delegation of some responsibilities characteristic of the welfare state to third-sector entities (Laurett & Ferreira, 2018), with a concomitant reduction in funds, privatization and decentralization of services (Carswell et al., 2012). States intervene on a national scale, but social problems go beyond borders, are globalized and multicultural (Escobar & Gutiérrez, 2011). In the profitable sector, companies have adopted more socially responsible and sustainable stances to respond to the demands of their stakeholders who are attentive to their practices (Carswell et al., 2012). Third-sector organizations find themselves in an increasingly competitive environment, and have to respond to growing social problems with less state funding (Faulkner et al., 2023; Pärl et al., 2022). Thus, they are forced to turn their practices to the market to obtain alternative forms of financing (Song, 2022; Zhu & Sun, 2020). They increasingly use the strategy of creating networks of partners that allow them to obtain added value (Escobar & Gutiérrez, 2011). It is in the context of this convergence of missions from the various sectors that a new entity emerges, the so-called fourth sector (Fourth Sector Network, 2009; Sabeti, 2011). The fourth sector is a new and promising sector of society, marked by a dual purpose: to generate profit and social impact by using different strategies, such as intersectoral collaboration and hybrid organizations (HO) (Escobar & Gutiérrez, 2011). As it is a relatively recent phenomenon, the fourth sector remains shrouded in ambiguity, with definitions dispersed amidst a sparse landscape of literature. Therefore, it is clear that we need a more holistic and collaborative approach, and in this study, we start from the following research proposition: The fourth sector arises from the intersection of the three traditional sectors, and it is defined by pursuing social objectives but with profit-making purposes (Fig. 1). This work aims to clarify the definition and frame the scope of its activity, generating a theoretical contribution to the existing knowledge on the fourth sector and main related concepts.

Fig. 1
figure 1

The fourth sector as the intersection of traditional sectors.  Source: Author’s creation, adapted from Sánchez-Hernández et al. (2021a)

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2 Literature review

In broad terms, the fourth sector refers to a new type of organization/model that exists alongside the traditional three sectors of the economy — the public sector, the private sector, and the nonprofit sector —, and is characterized by its focus on social and environmental impact, rather than solely on profit (Rask et al., 2020). There are currently three main approaches (see Table 1) that use the designation fourth sector, despite having very different characteristics.

Table 1 4th sector strings.  Source,  Author’s creation, based on several authors (Raisio et al., 2019 ; Rask et al., 2018 ).
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The first approach (Williams, 2002, 2005) associates the fourth sector with informal volunteering (IV), also called one-on-one, which is distinct from that associated with third-sector organizations (Heley et al., 2022). It is characterized by a spontaneous movement of people towards their community.

The second approach, Hybrid Organizations (HO), is in line with our research proposition. It is the most devoted to organizations that do not purely belong to any traditional sector. It arises from the premise that today’s most significant social problems cannot be addressed without the participation of the three traditional sectors (Escobar & Gutiérrez, 2011; Sánchez-Hernández et al., 2021a, b). It is in this proximity of missions from the various sectors that a new entity emerges, the so-called fourth sector. In this approach, it is defined as “a new protagonist in the socioeconomic sphere that results from the convergence of various sectors in organizations and business models that seek to respond to social and environmental problems through social innovation” (Escobar & Gutiérrez, 2011, p33). In this approach, the fourth sector revitalizes the concept of the social economy (Ávila & Campos, 2018) by encompassing the traditional sectors (Rubio-Mozos et al., 2019). Under the hybrid business string (Zurbano et al., 2012), the identification of the fourth sector generally applies to one of the following alternatives:

  • i) Social organizations with economic results: Organizations that generate economic and social value in the market, such as social enterprises (Borzaga et al., 2020), but also traditional companies with aspirations that identify themselves as companies that go beyond classic CSR.

  • ii) New ways of doing business (from the point of view of positive social and environmental impact), and those entities in the public sphere that try to be more oriented to the specific needs of people, but also those that intend to innovate regarding the participation and involvement citizens in the co-creation of public services by using market methods (Sánchez-Hernández et al., 2021b).

The third approach, called self-organized civic activism (SOCA), refers to civic movements spontaneously generated in the community that use new technologies and social networks (Raisio et al., 2019). According to Rask et al. (2018), its main characteristics are spontaneity, great dynamism, the absence of bureaucracies, a horizontal structure without hierarchies, and dissociation from formal organizations. The same author states that these movements are criticized for their potential risk, since these are initiatives based on goodwill, but lack knowledge and coordination.

According to Rask et al. (2018), these various approaches can be summarized to try to find an integrative perspective, by considering them as a growth regarding the level of organization and stability over time. The integrative definition is the following: “the fourth sector is an emerging field, composed of actors or actor’s groups whose foundational logic is not the representation of established interest, but rather, the idea of social cooperation through hybrid networking” (Rask et al., 2018 p.46).

To sum up, the fourth sector works in a spectrum of HO. At one end of the spectrum there are third-sector organizations with profitable activities, social enterprises at the center and, at the opposite end, companies whose activity has significant social impact. These organizations bear characteristics such as greater or lesser presence in the market, and different degrees of focus on social concerns (Fourth Sector Network, 2009). These HO have a dual purpose: on the one hand, they are economically viable and, on the other hand, their purpose goes beyond profit and seeks ethical and sustainable goals, as well as creating benefits through their activities for society as a whole and the planet (Rubio-Mozos et al., 2019). Sabeti (2011) summarizes some of these characteristics: having a social purpose, a business method, transparency, social and environmental responsibility and giving fair compensation to employees. These main arguments consider that can generate returns for investors and shareholders if they do not jeopardize their ability to act in favor of their mission. These hybrid entities combine the best that each of the traditional sectors has to offer, in order to respond to shared social objectives in a sustainable and lasting way, through social innovation (Avidar, 2017; Escobar & Gutiérrez, 2011; Sánchez-Hernández et al., 2021b). Sabeti (2011) considers that these HO feature a new model of entrepreneurship, developed by entrepreneurs motivated by social causes, which are not exclusively profitable or non-profitable, and can be called “for benefit”, since they generate income, but prioritize the social mission, acting in a variety of areas, such as poverty, social exclusion, health, decent work, among others. In the fourth sector, initiatives can exist without a formal organizational structure, constituting themselves merely as “entities” that fill the empty spaces left by traditional sectors and also as forms of cooperative and networked functioning (Escobar & Gutiérrez, 2011).

The fourth sector can be considered a transition towards sustainable businesses by introducing social purpose into the strategic management line of organizations (Rubio-Mozos et al., 2019). To sum up, and according to the Ibero-American Secretariat General of the IE University, the fourth sector “is a complement, not a substitute, to the other sectors” (IASG, 2019, p. 21) that works to achieve the Sustainable Development Goals (SDGs) by 2030. Consequently, sustainability is the heart of the emerging fourth sector. At this point, it is important to mention that it can be challenging to measure the performance and the impact of the fourth sector (Núñez-Barriopedro & Llombart Tárrega, 2021), as it may involve intangible outcomes, such as increased social cohesion or improved quality of life. As such, it is important for organizations in the fourth sector to be transparent about their impact measurement processes and to continuously strive to improve the quality and reliability of their data.

In general, the distinction between the third and fourth sectors lies in their fundamental purposes, organizational structures, and orientations towards profit and social impact. The third sector, often referred to as the nonprofit sector, comprises organizations that operate primarily to address social, environmental, or cultural needs, rather than to generate profit. These organizations, including charities, non-governmental organizations (NGOs), and community groups, typically rely on donations, grants, and volunteer efforts to sustain their operations (Stühlinger & Hersberger-Langloh, 2021). The third sector plays a crucial role in filling gaps left by government and business in addressing societal challenges and advocating for social change.

The fourth sector represents a novel paradigm that bridges the gap between traditional for-profit and nonprofit sectors by integrating social and environmental objectives into business models (Piedrahita et al., 2021). Fourth-sector organizations, which might be dubbed as social enterprises or impact-driven businesses, aim to generate revenue while simultaneously addressing social or environmental issues (Martins et al., 2021; Rask et al., 2020). They operate under a hybrid model that emphasizes both financial sustainability and positive social impact. The fourth sector encompasses a wide range of entities, including B Corporations (B Corps), social purpose corporations, and cooperatives, all of which prioritize the triple bottom line — people, planet, and profit.

While the third sector focuses primarily on addressing social needs through philanthropy and community service, the fourth sector represents a more integrated approach to social change by leveraging market mechanisms and entrepreneurial strategies. Both play vital roles in advancing social progress and addressing complex challenges, but they differ in their approaches to resource mobilization, governance structures, and models of social impact (Sanzo-Pérez et al., 2022; Zhu & Sun, 2020). As the boundaries between sectors continue to blur, understanding the distinctions and synergies between the third and fourth sectors is essential for developing effective strategies to address pressing global issues and promote sustainable development.

3 Methodology

We used an innovative approach by combining a very specific literature review with the opinion of experts on the topic via a similarity analysis. Our research is based on a qualitative methodology, using content analysis performed through the IRaMuTeQ software. Content analysis is a research method used in qualitative studies and encompasses different techniques to generate knowledge in a systematic and rigorous way, based on textual information generated during the investigation (White & Marsh, 2006). In the context of the IRaMuTeQ software, similarity analysis refers to the examination of similarities or patterns within textual data, particularly in qualitative analysis, such as text mining and content analysis (Camargo & Justo, 2013). The software employs various techniques for lexical analysis, including frequency counts, co-occurrence analysis, and concordance analysis; subsequently, similarity is measured and the software offers visualization tools to represent it graphically. The similarity analysis involves a method called Hierarchical Cluster Analysis (HCA), which we will use in our analysis, and the software arranges the data into a hierarchy of clusters based on their similarities. At each step of the process, the algorithm merges the two most similar clusters, until all data points are grouped into a single cluster.

A qualitative methodology combining content analysis and expert interviews can be well-suited to achieve the objective of contributing to the theoretical knowledge (Döringer, 2021) on the fourth sector by clarifying its definition and framing its activity, because (i) this allows exploring deeply into the content of papers and interviews, potentially uncovering nuances, patterns, and themes within the data that may not be apparent through quantitative methods; (ii) as a relatively new and evolving concept, the fourth sector requires an exploratory approach; (iii) by analyzing the content of relevant papers and conducting interviews with experts, we gain a deeper understanding of how the fourth sector is conceptualized, operationalized, and practiced in different contexts and settings, and this contextual understanding is crucial for framing the activity of the fourth sector within its socio-economic, political, and cultural contexts.

The selection of articles included in the sample is presented in Fig. 2. At first, the Web of Science (WoS) database was used to search for the term “Fourth Sector”, resulting in a total of 31 results over the period from 1996 to 2023. Only scientific papers were included in the sample. After a brief reading, all those papers that did not correspond to the concept under study were excluded. This selection resulted in 13 papers, dated from 2011 to 2020, associated to the database through the areas of study of management, economics, sustainability, and public policies (Appendix 1). Finally, the abstracts of these papers were formatted in a document that constitutes the textual corpus, imported to the IRaMuTeQ program and subsequently analyzed. To understand which concepts stand out in the summaries of the literature analyzed and the relationship between them, a similarity analysis was carried out, the result of which can be seen in Appendix 2.

Fig. 2
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Selection of articles included in the sample

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Subsequently, written interviews were conducted, consisting of two open-answer questions to seven academic specialists regarding the definition of the fourth sector, its main characteristics, and what distinguishes it from more traditional sectors of activity, as well as a practical example of what that could be considered a fourth sector entity. These specialists were selected through the snowball sampling method to complete the data obtained through the literature review. Firstly, we identified two specialists and sent them emails because of their research proximity to this topic under study. We requested them to respond to our questions and to recommend a colleague who works closely on the topic. We ceased the identification of new specialists upon reaching saturation, meaning that we began to hear the same themes, patterns, or information repeatedly across the interviews. This indicated that the data collection process had sufficiently captured the range and depth of experiences or perspectives related to the research topic. We had 4 Portuguese and 3 Spanish experts, from the areas of economics (3), geography (2), social economy (1) and marketing (1), as we can see in Table 2. These data were added to the initial textual corpus, and a new similarity analysis was generated (see Appendix 3); the insertion of the data regarding the experts’ interviews has caused some changes in the similarity analysis.

Table 2 Fourth sector specialists’ sample: descriptive analysis
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4 Results

The data collected originated two similarity analysis. Similarity analysis A (Appendix 2) refers to the content of the abstracts of the papers included in the sample, and similarity analysis B (Appendix 3) cumulatively encompasses the textual data of the papers and the answers to the interviews carried out with experts on the field of the fourth sector. The interviews were completely transcribed and added to the software.

4.1 Similarity analysis A

The abstracts of the articles included in the analysis originated 3 clusters with 11 distinct related sections. The sections are potential thematic or conceptual grouping of textual data that identify patterns and /or relationships. Two of the clusters were equivalent to the previously identified theoretical frameworks (HO and IV), and the third one was devoted to the third sector (TS cluster). The number of occurrences for the same word ranged from 18 to 3.

1st) HO cluster, including most of the sections:

  • Section 1– The central concept is the research term “fourth sector”, either because it is the most frequent (18 times), or because it has the most sections that are directly associated with overlapping (5 times in total). Associated with the concept “fourth sector”, there is the word “emergence” (4 times). Also directly associated with this are words that refer to the various traditional sectors of activity, namely “government”, “third sector” and “company”. The word “company” occurs a total of 16 times, and it is the central concept of Sect. 2, responsible for bridging the gap between Sect. 1 and several other Sects. (3, 8, 9, 10, 11). Less expressiveness is found for the concepts “government” and “third sector”, with 3 and 4 occurrences, respectively, thus occupying a secondary position within this section. Also noteworthy is the word “purpose” associated with the “fourth sector” concept.

  • Section 2 – The word “company” is very central, and we have the word “contribute” (7 occurrences) linked with “planet” (4); “person” (4) and “community” (3). Concepts related with sustainability concerns are “sustainability” (6) “sustainable development goals” (8) “corporate social responsibility” (4), and “sustainable strategic management model” (3) feature prominently in this section, and are shared with the adjacent Sects. 3 and 4.

  • Section 3– Highlights the intersectoral relationship characteristic of one of the trends in the fourth sector. The most prominent concept is “business”, centrally positioned between the concepts “for-profit” (7) and “nonprofit” (5). The term “nonprofit” branches out into concepts such as “for-benefit” (4), “benefit corporation” (6), “structure” (8), “legal” (3) and “entrepreneur” (5). From the concept “for-profit”, words such as “environmental” (4), “social” (8) and “economy” (4) are linked through the word “combine”. This section highlights the dual purpose of the fourth sector to generate profit and social impact.

  • Sections 4 ,5 ,6 ,7 – These represent examples of fourth-sector initiatives, such as the protection of coral reefs (Cruz-Trinidad et al., 2011) and collaboration between universities, industry and technology in Saudi Arabia (Shin et al., 2012). As they are specific cases in the literature, the concepts that represent them have little prominence in the general panorama, and are notable for their small frequency and ramification.

2nd) TS cluster, including the following 3 sections:

  • Section 8 – Emerges as a transition section between the sections of empirical approach to the fourth sector (1, 2, 3) and Sects. 9 and 10, which feature theoretical content. As concepts of connection to the first group, words such as “sustainable development goals” (8) and “management” (5) can be highlighted, which branch out into theoretical concepts, such as “model” (12) and “academic” (5).

  • Sections 9 and 10 – These are theoretical sections, featuring “notion” (14) and “concept” (16) as central concepts.

3rd) IV cluster for one isolated section: 

  • Section 11 – This is one of the most distant sections from Sect. 1. It does not share concepts or overlap with any other section. It is linked to Sect. 3 through the word “public” (10), which will branch out to the concept “policy” (14). At the far end appear concepts related to the definition of the fourth sector presented by Williams (2002), which refer to informal volunteering, namely “micro-volunteering” (6) and “volunteering” (4).

The HO cluster is the most important one. It should be noted that of the 3 traditional sectors of activity, the most referred to is the private sector, with a high frequency of words: “company” (16), “business” (10), “for-profit” (7), “corporate” (4), “corporate social responsibility” (4), and “private” (4), with a total of 45 references. Even so, the reference to the involvement of the three traditional sectors are clear, which, given the new dynamics of action, gives rise to the fourth sector. On the side of the public sector, we can find occurrences of several terms such as “policy” (13) “public” (8) and “government” (1), with a total of 22 references. Non-profit organizations are represented by terms such as “social economy” (9), “social” (10), “nonprofit” (5), “third sector” (4), in a total of 28 references.

4.2 Similarity analysis B

The insertion of data related to the interviews with experts in the previous textual corpus presents some remarkable modifications:

In similarity analysis A, there were 11 sections, while B is composed of 12. The term fourth sector lost some of its centrality, and now there are two distinct groups. Thus, the HO cluster involving the term “fourth sector” (Sect. 1) is spatially separated from a new cluster (HO business) involving the concept of “business” (3-a).

Section 3, whose most prominent terms is “business”, undergoes changes compared to the previous similarity analysis, and concepts that lacked great prominence in this section, gain greater preponderance in this new analysis, giving rise to 3 distinct and overlapping Sect. (3-a, 3-b, and 3-c). Section 3-c has as its central term the word “social”, and Sect. 3-b the word “for-profit”, which denotes that there is a subdivision of types of business, some pursuing a social purpose and others an exclusively economic purpose.

Section 4 in the first analysis ceases to exist as an autonomous section and the words that constitute it are integrated into Sect. 3, thus losing relevance. This was expected, as experts were informing about the topic but avoiding examples or specific practical evidence. These words were mostly related to a particular case study, having little impact on the overall picture.

Section 11 subdivides into Sect. 1-a and Sect. 1-b (a new cluster for the relationship between the public and the private sector, the PL-PR cluster). In addition, Sect. 1-a continues to encompass the definition of the fourth sector as informal volunteering. Section 11-b, which is the new PL-PR cluster, becomes the transition section between Sect. 1 “fourth sector” and Sect. 3-a “business”. The central words are “sector”, “public” and “private”, and the supporting word “integrate” also appears, coming from the concept “third sector” that appears at the far end of Sect. 1 “fourth sector”. This list of words once again suggests the intersectoral collaboration of the fourth sector.

The connection of Sect. 1 “fourth sector” to transition Sect. 1-b (“private” and “public”), and subsequently to section business, is the word “third sector”, suggesting that it is particularly this sector that makes the connection between everyone and enhances their collaboration in market initiatives.

5 Discussion

Analyzing the two similarity analyzes, it is possible to verify the prominence of terms such as “emergence”, defined as the emergence or becoming prominent, directly associated with the term “fourth sector” denotes the novelty that it constitutes.

One of the objectives of this research was to clarify the definition of the fourth sector, and the results obtained point to the majority trend in the scientific literature to use the term as a spectrum of hybrid organizations (HO). In the similarity analyses, concepts that could be associated with the fourth sector, such as self-organized civic activism (Rask et al., 2020), were not evident. Therefore, in the context of the fourth sector, civic activism underscores the idea of citizen-led efforts to drive social innovation and impact, thus blurring the lines between traditional sectors and fostering collaborative, community-driven solutions to complex problems, although this bottom-up approach was not clearly present in the similarity analyses.

The definition of the fourth sector as informal volunteering was mentioned in a single paper, and therefore is of little significance for the results, with only two associated terms — “micro-volunteering” (6) and “volunteering” (4). In these cases, the term fourth sector is used as a synonym for informal volunteering (Williams, 2002, 2005), and, more recently, it has been used in the context of organizations that promote social good through business initiatives (Cuthill & Warburton, 2005). In this context, informal volunteering (individual-based help) is as prevalent as formal volunteering (group-based help), and is predominant among deprived populations, although the third-sector approach should be complemented by a fourth-sector approach that focuses on one-to-one aid, because while affluent populations engage more in voluntary groups for social reasons, lower-income groups rely heavily on one-to-one aid to improve their material circumstances (Williams, 2002). Nevertheless, the scarcity of more recent papers that support the definition of informal volunteering is quite evident. Therefore, the data obtained in this research corroborate the idea that the definition of the fourth sector as informal volunteering is in disuse.

The presence of terms related to the three traditional sectors of activity, which appear in various sections, related to each other and associated with the concept of fourth sector, are a contribution to the premise that the growing dimension and complexity of emerging socioeconomic problems greatly exceeds the capacity of organizations, and the public, private and social sectors alone are not able to generate adequate responses (Austin & Seitanidi, 2012). Thus, organizations from various sectors (public, private and social) are pressured to collaborate in multi-sector partnerships (MacDonald et al., 2019). However, the presence of terms such as “business” and “company” is obvious, which could suggest a special focus on the private sector. These terms are associated with words such as “for-benefit”, denoting the central role of HO in the fourth sector. Despite having a strong focus on the market, these are a new model of entrepreneurship, developed by entrepreneurs motivated by social causes — which are not exclusively profitable or non-profitable — and are called for-benefit, as they generate income and prioritize the social mission, acting in a variety of areas such as fighting against poverty, health, environment, among others (Sabeti, 2011). Therefore, the data are suggestive and present a fourth sector that does not fully overlap with the concept of multi-sector partnerships. In addition to the convergence of missions and planned joint action, the existence of profitable activity and focus on social problems seems to be essential for it to be considered an entity in the fourth sector. This same perspective is mentioned in the literature (Wilburn & Wilburn, 2014) when referring to the fourth sector as a new business model that enables a structure that helps (1) the expansion of third-sector organizations, (2) a profitable sector whose activity is intrinsically linked to social responsibility, and (3) entrepreneurs who intend to invest in businesses committed to transforming society. Despite this evidence, another explanation for the prominence of terms related to the profit sector is the fact that market-oriented organizations, such as the Benefit Corporation (Koehn & Hannigan, 2016), are more legally supported than others (e.g., networks and multisectoral partnerships), thus being easier to identify and study, and therefore resulting in a greater number of scientific papers.

The results found seem to suggest that the main role of the public sector in the fourth sector is the creation of policies and laws that regulate this sector. This focus on the “policy” concept may be due to the existence of three papers by the same author (Rubio-Mozos et al., 2019, 2020a, b) in a small sample. The authors advocate the need for a systemic approach, including governments, the academic community, the entities of the fourth sector and civil society. The proposed approach is called “4s SME’s engagement ecosystem”, which involves small and medium-sized companies in the fourth sector. The aim is to contribute to its development and the measurability of this “sustainable welfare economy”. Other authors corroborate this emphasis on the inexistence of basic policies for this sector. This trend has emerged organically, without a base structure to support it (Fourth Sector Network, 2009), and there is no environment prepared with adequate legislation, market regulation, accountability systems, among others, that are specific to this new sector of activity (Sabeti, 2011). The inexistence of these specificities will force entrepreneurs to fit into existing structures for other sectors, thus blurring their mission and objectives, increasing the bureaucracy and complexity of structures, and unnecessary expenditure of resources, resulting in a competitive disadvantage (Fourth Sector Network, 2009).

Economic, social and environmental sustainability were highlighted in the results obtained, and have been mentioned before (Ávila & Campos, 2018; Rubio-Mozos et al., 2019; Ventura, 2020). The fourth sector can catalyze society’s role in the pursuit of sustainability (Carswell et al., 2012), which is defined as “the development that seeks to respond to the needs of the present without compromising the capacity of future generations to respond to their own needs” (United Nations, 1987). Carswell et al. (2012) state that sustainability is triple bottom-line, requiring a balance between people, the planet and profit, and these same words were found in our similarity analyses. Although the two similarity analyses are relatively overlapping, there is something significant that differentiates them. There is a more marked separation between the “fourth sector” section and the “business” section, with the bridge being mediated by the term “third sector”, which will produce an island cluster, which includes the terms “public” and “private”. To note that the first similarity analysis was performed using international data, with papers from Europe, Asia, and America, while the second one includes data provided exclusively by Spanish and Portuguese specialists. As mentioned above, there is specific legislation at the international level that directly relates the fourth sector to the market, such as benefit corporations. However, this type of legislation does not exist in both countries, where the tradition of social causes is closely related to the third sector. Thus, it seems that, in Spain and Portugal, this fourth sector appears to be mediated by the third sector, which forms the bridge between the third and the public and private sectors. Thus, it seems that the second similarity analysis reflects the culture and legislation of both countries, in the sense that it gives greater prominence to the third sector as the main player in the emergence of the fourth sector. Two of the articles included in the sample (Cruz-Trinidad et al., 2011; Shin et al., 2012) refer to case studies that have little impact on the presented sections, even lacking associated concepts in similarity analysis B.

6 Conclusions and limitations

This study suggests that both the literature review and the opinions of experts converge to affirm that the definition of the fourth sector as a spectrum of hybrid nature organizations is the most accepted approach on the topic. The definition of the fourth sector as voluntary actions seems to be currently out of favor. Finally, there is no clear evidence of the association of the fourth sector with any kind of civic activism.

The results obtained corroborate the fourth sector as an emerging sector made up of actors from the three traditional sectors (public, private and third sector) that collaborate closely with each other. The focus on the business, especially from the experts’ side, is evident, and this practice seems to be the main factor that defines belonging to this sector. However, profit is not an objective in itself, as there must be a social purpose arising from the activity. The data obtained suggest that the main contribution of the public sector to the fourth sector is the creation of policies that legally frame its activity.

The widespread emergence of the fourth sector offers great potential that still remains largely untapped. Contrary to the American model, social enterprise in Europe and neighboring nations arises primarily from ingrained organizational structures and values intrinsic to European societies (Borzaga et al., 2020; LaVoi & Haley, 2021). These values encompass solidarity, self-help, participation, and the pursuit of inclusive, sustainable growth. Consequently, social enterprise thrives as a collective endeavor, embodying a communal entrepreneurial spirit. Many EU Member States exhibit imbalanced ecosystems, often neglecting critical components, such as capacity-building, networking, and cooperation. Therefore, a holistic ecosystem must prioritize improving public procurement processes (Borzaga et al., 2020).

The concept of sustainability closely intersects with the fourth sector, which represents a hybrid sector that blend elements of the public, private, and non-profit sectors. The SDGs established by the United Nations provide a framework for addressing global challenges, such as poverty, inequality, and climate change. Achieving the SDGs requires the active participation of various sectors, including government, civil society, and the private sector, namely the emerging fourth sector. Therefore, in this context, the fourth sector plays a crucial role in advancing sustainable development by integrating social, environmental, and economic considerations into its practices. Organizations operating within the fourth sector strive to create positive impact across multiple dimensions while ensuring long-term viability and resilience (IASG, 2019).

This study was delimited by specific keywords to guide the research, and therefore this targeted approach may not capture the totality of the scholarly discourse within this field. The main difficulties of our research were the limited number of papers available in the WoS database at the time of survey, which weakens the robustness of the results obtained, and consequently of the conclusions presented. We can also mention limitations related to the interviews, like the existence of preconceptions that might have influenced the answers, as well as the social desirability bias, where interviewees may have given answers that they believe are socially acceptable rather than reflecting their true thoughts or experiences.

However, the scarcity of research papers dedicated to the fourth sector justifies the analysis and makes this article a valuable contribution to shed light on this emerging field. We understand that having done the research only in the WoS database, despite its extensive citation analysis tools, has some limitations that might affect the comprehensiveness of the literature available on a given topic. Therefore, future research might include other databases and other classification criteria to ensure a more comprehensive and wide coverage.