Philosophers have traditionally held that propositions mark the domain of rational thought and inference. Many philosophers have held that only conceptually sophisticated creatures like us could have propositional attitudes. But in recent decades, philosophers have adopted increasingly liberal views of propositional attitudes that encompass the mental states of various non-human animals. These views now sit alongside more traditional views within the philosophical mainstream. In this paper I argue that liberalized views of propositional attitudes are so liberal that they encompass states of all sorts of apparently mindless systems like circadian clocks in plants. I begin by arguing that on the most well-developed and widely endorsed theories of underived representation in philosophy, circadian clocks qualify as representations. I then argue that standard reasons for thinking that perceptual states and pictures have propositional content carry over to circadian clocks. Finally, I argue that circadian representations in plants play the kind of functional role that is widely taken to be partly constitutive of belief-like attitudes. So according to mainstream theories of representation, propositions, and attitudes, plants have propositional attitudes. Yet on other more traditional views, this conclusion would seem absurd. So, contrary to appearances, there is no shared, stable understanding of what propositional attitudes are in contemporary philosophy.
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As I hope will become clear later, I am not here intending to cast a skeptical light on the extensional adequacy of these scientific distinctions (here, at least). The question I am interested in is whether the notion of a propositional attitude is empirically grounded enough to capture these distinctions.
I recognize that several philosophers and biologists have recently drawn from the scientific literature on ‘plant intelligence’ to argue that plants indeed have minds (Maher 2017; Gagliano 2017; Calvo 2017). I don’t dispute this claim here. I largely prescind from empirical theses in this paper to explore the commitments about different views of propositional representation.
See Ben-Yami (1997) for a sense of just how thin the historical reasons for thinking that mental states are propositional attitudes really were.
I am here just reporting a dominant line of thought, not endorsing it. For some critical discussion of this way of conceptualizing and naturalizing intentionality, see Morgan and Piccinini (2017).
I cannot do justice to the important differences between the views that I am classifying as tracking theories within the scope of this paper. That it is reasonable to treat these theories as variations on the same basic theme is now widely assumed in the literature (Burge 2010; Kriegel 2012; Mendelovici, 2013). I say more by way justifying this assumption in Morgan (forthcoming), where I also argue that Burge’s (2010) influential view, which is trenchantly opposed to tracking theories, is simply another variant of this same basic theme.
From the Latin ‘circa’ (approximately) and ‘diēm’ (day).
I put ‘day’ in quotes because I am writing not of actual daytime, but of represented daytime. In the biological literature, this distinction is standardly marked by writing of ‘subjective’ day or night. This underscores the general point that it is difficult if not impossible to explain clock-mediated behavior without positing representational content.
It is not clear that clocks are literally ‘selected’ to play control functions here, but it is not clear that neurons are literally ‘selected’ in the process of animal learning either (Crick 1989; Quartz and Sejnowski 1997). The notion of selection is at best an illustrative metaphor for Dretske. What is theoretically important for him is simply the idea that content plays a role in explaining the behavior of individual organisms.
Note that when I write of ‘pictures’ and ‘pictorial content’ here, I specifically have in mind the representational features of pictures. Not all pictures are representational in the sense that they purport to depict some specific state of affairs, and even those that are might be said to have a kind of non-representational expressive or affective content. Like Crane, I focus only on the representational features of pictures.
Crane has an independent line of argument against the propositional view of pictorial content, based on the idea that pictures do not stand in the logical relations that propositions necessarily do. Grzankowski (2015) ably shows that this rests on another vehicle-content confusion, so I needn’t engage with this argument here.
One might also hold that plant clocks play a desire-like, telic role since they serve to guide the plant’s activities. In that case they would qualify as what Millikan (1995) calls ‘pushmi-pullyu’ representations. I am not primarily concerned in this paper to identify precisely what kind of attitudinal role plant circadian clocks play; my main goal is just to show that they play some such role or other. I should note that nothing I say here provides reason to think plants can have several different kinds of attitude. Interpretivists would reject ‘punctate’ propositional attitudes on grounds that attitude ascription is necessarily holistic (Davidson 1973), but I think most of the realists I am engaging with here would admit the possibility of punctate attitudes. Still, some might deny this. As I’ll go on to discuss shortly, realists might invoke various reasons for resisting the conclusion that plants have genuine attitudes—but in doing so they’re bound to make assumptions that other realists would find deeply implausible.
Chisholm appealed to a third criterion, but this is not relevant for my purposes so I leave it out for the sake of expository clarity.
I remain officially neutral on the question of whether this implies that capacities like inference are ubiquitous in nature, or that standard views of such capacities are empirically inadequate. I happen to believe the latter, but this biographical fact is irrelevant to the conditional thesis of this paper.
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Morgan, A. Pictures, Plants, and Propositions. Minds & Machines 29, 309–329 (2019). https://doi.org/10.1007/s11023-018-9483-4
- Circadian clocks
- Perceptual content
- Plant intelligence
- Propositional attitudes