Mele has presented several statements of the Zygote Argument since it was first introduced, and it will be useful to adopt an intuitive way of tracking them. With that aim in mind, I will hereafter refer to statements of the Zygote Argument by the year they first appeared in print, starting with “ZA-2006” to label the very first statement of the Zygote Argument (Mele 2006).Footnote 8 My invalidity objection targets a later statement of the Zygote Argument that Mele put forward in response to criticisms of ZA-2006, hereafter “ZA-2012”Footnote 9:
P1. Ernie is not [free or] morally responsible for anything he does.
P2. Concerning moral responsibility of the beings into whom the zygotes develop, there is no significant difference between the way Ernie’s zygote comes to exist and the way any normal human zygote comes to exist in a deterministic universe.
C. So determinism precludes [free will and] moral responsibility – at least for human beings who develop from normal human zygotes. (Mele 2012: 15)Footnote 10
ZA-2012 is invalid: its premises entail merely that it is metaphysically impossible for a normal human born from a human zygote to act freely and morally responsibly when determinism is true, but its conclusion says that it is owing to determinism that people lack free will and moral responsibility when determinism is true.Footnote 11
So understood, we can say that ZA-2012 is invalid because its premises support only (an idiosyncratically restricted variant of) the incompossibility solution to the correlation problem, but its conclusion forwards a controversial causal luck solution to (E2) of the explanation problem.
Having shown that ZA-2012 is fallacious, I outlined two ways to improve the original Zygote Argument, saying:
[T]here are two ways that one might repair the argument. The simplest repair strategy is to weaken the original conclusion so that the Zygote Argument concludes to mere incompossibilism [i.e. the thesis that deterministic laws and free action are incompossible]. However, if the original, explanatory conclusion of Mele’s argument is to be defended, the Zygote Argument must be amended to include a premise that identifies deterministic laws as a freedom-undermining feature of the manipulation story. (Mickelson 2015b: 2912; my emphasis)
Here, I propose two distinct strategies for responding to the invalidity objection. First, one may hold the two premises of ZA-2012 fixed and change its solution to the incompossibility thesis entailed by those premises. For clarity, let us call any argument which results from implementing this “simplest repair” strategy a premise-preserving solution to the invalidity objection. Second, one may keep the premises of ZA-2012 fixed and update its premises so that they support this explanatory conclusion in order to create a variant of the Zygote Argument which is invulnerable to my invalidity objection. Let us call any argument which results from this strategy a conclusion-preserving solution to the invalidity objection. Notably, I argue that the only dialectically felicitous way to develop a conclusion-preserving solution to my invalidity objection is to supplement ZA-2012’s original premises with a best-explanation argument (Mickelson 2015b: 2912).
From the outset, I worried that philosophers might be tempted to brush off my complaints about the invalidity of ZA-2012 given how easy it is to develop a new, valid variant of ZA-2012 using the premise-preserving strategy (Mickelson 2015b: 2917). My proposed premise-preserving variant of the Zygote Argument, hereafter “Simple Repair,” may be summarized as follows:
P1. Ernie does not freely A and is not morally responsible for A-ing.
P2. Concerning free action and moral responsibility, there is no significant difference between Ernie’s A-ing and any candidate for a free and morally responsible action in a deterministic universe.
C. So, no normal human candidate for a free and morally responsible action in a deterministic universe is a free action nor an action for which the actor is morally responsible. (Mickelson 2015b: 2917-2919)
In response to the invalidity objection and my overview of the two response strategies,Footnote 12 Mele adopted the following premise-preserving variant of ZA-2012, hereafter “ZA-2013”:
P1. Ernie is [not a free agent and is] not morally responsible for anything.
P2. Concerning [the free action and] moral responsibility of the beings into whom the zygotes develop, there is no significant difference between the way Ernie’s zygote comes to exist and the way any normal human zygote comes to exist in a deterministic universe.
C. So in no possible deterministic world in which a human being develops from a normal human zygote is that human being [free or] morally responsible for anything he or she does (Mele 2013: 176).
Mele has recently reaffirmed his commitment to the premise-preserving strategy in his restatement of ZA-2013 as a modus ponens argument that I will call “ZA-2019”:
P1. Ernie is not [a free agent or] morally responsible for anything he does.
P2. If Ernie is not [a free agent or] morally responsible for anything he does, no human being who develops from a normal human zygote in a deterministic world is morally responsible for anything he or she does.
C. So in no possible deterministic world in which a human being develops from a normal human zygote is that human being [a free agent or] morally responsible for anything he or she does. (Mele 2019: 120-121)
ZA-2019 is, uncontroversially, a valid argument.
Mele presents ZA-2019 in response to the worry that ZA-2013 is invalid.Footnote 13 Mele’s attention to this invalidity objection is somewhat puzzling. Mele offers no evidence that any professional philosopher has had this sort of worry about the validity of ZA-2013, nor does he mention that multiple free-will specialists (e.g. Mickelson 2015b: 2917, n.6; Sartorio 2016: 163–164) had already addressed this “worry” by pointing out that arguments such as ZA-2013 may be represented as modus ponens arguments. Moreover, Mele’s attention to this relatively trivial invalidity objection to ZA-2013 might confuse the average reader, for he does not distinguish it from my invalidity objection to ZA-2012—which is noteworthy because restating ZA-2013 as ZA-2019 does not address my invalidity objection.Footnote 14
To stave off needless confusion, let us draw a clear line between my invalidity objection to ZA-2012 and Mele’s trivial invalidity worries about ZA-2013. Hereafter, let the latter type of invalidity objection be known as the logic-text objection, since it amounts to little more than the (arguably misguidedFootnote 15) complaint that Mele should have stated ZA-2013 as a logic-text proof in classical deductive logic from the outset (rather than leaving this simple task as an exercise for his readers). By contrast, when an argument is invalid because it fails in its aim to close the “explanatory gap” between an incompossibility solution to the correlation problem and a specific solution to (E2) of the explanation problem, I will call it an explanatory gap objection.Footnote 16
While I grant that ZA-2013 and ZA-2019 are valid arguments, I do not think that Mele has, by adopting these new variants of ZA-2012/ZA-2006, adequately responded to the explanatory gap objection. Even if sound, ZA-2013 and ZA-2019 do nothing to adjudicate between the rival candidate explanations for the incompossibility of deterministic laws and free human agents. I have motivated this point by demonstrating that ZA-2013 may be used as a foundation for a more sweeping generalization argument which concludes that free will is impossible due entirely to constitutive luck, from which it follows that a strict constitutive luck solution to (E2) is true, that the causal luck solution to (E2) promoted by ZA-2012 is false, and that the conclusion of ZA-2013 expresses a true but metaphysically arbitrary claim (Mickelson 2015b; see also Mickelson 2017, 2019a, and 2019b). To be clear, I have never proposed that ZA-2013 is invalid, unimportant, or otherwise uninteresting; I have simply pointed out the generally overlooked fact that the premises of ZA-2012 fall short of delivering a broadly causal luck solution, or any solution whatever, to (E2).Footnote 17 This observation does not suggest that the Zygote Argument is unworthy of attention, but it does suggest that the underlying logical structure and upshot of manipulation arguments are poorly understood and, so, are worthy of considerably more attention than they have been given.
De Marco (2016) enters the debate at this point, claiming that he has devised two ways to “rescue” the Zygote Argument from my explanatory gap objection:
According to Mickelson, the only way to make such arguments valid is to supplement them with an argument that is an inference to the best explanation. In this paper, I argue that there are two other ways in which the proponent of such manipulation arguments can modify their argument, neither of which requires an inference to the best explanation. (De Marco 2016, abstract; my emphasis)
Pace De Marco, this summary of my position is flawed. It is not true that I say that the only way to change the invalid ZA-2012 into a valid argument is to “supplement them with an argument that is an inference to the best explanation.” As already discussed, I clearly outlined two ways to repair ZA-2012 in the face of the explanatory gap objection in Mickelson 2015b, namely the premise-preserving strategy and the conclusion-preserving strategy. I did claim that the only way to a conclusion-preserving solution to the explanatory gap objection to ZA-2012 is to add a best-explanation argument, but I also explicitly describe a premise-preserving solution that does not involve best-explanation reasoning of any kind (namely, “Simple Repair” above).
De Marco’s mischaracterization of my position is important when we look at his “two other ways” to repair manipulation arguments which are vulnerable to the explanatory gap objection.Footnote 18 De Marco summarizes his “initial solution” to the explanatory gap objection as follows:
For those manipulation arguments that are invalid for the reasons that Mickelson gives [i.e., those that are subject to an explanatory gap objection], as well as for the Zygote Argument, an easy fix would be to change their conclusion to the claim that compatibilism is false. (De Marco 2016:1624, my emphasis)
Since De Marco stipulates his own definition for the term ‘compatibilism’ in the course of his 2016 essay, it is important to note that he uses the phrase “compatibilism is false” to pick out the following incompossibility thesis:
there is no possible universe in which deterministic laws obtain and someone who is subject to the laws performs a free action (De Marco 2016: 1624).Footnote 19
So, piecing things together, De Marco’s “initial solution” to the explanatory gap objection consists in the following premise-preserving variant of ZA-2012, call it “Easy Fix”:
P1. Ernie does not act freely or responsibly.
P2. With regard to free action and moral responsibility, there is no significant difference between Ernie and a standard agent (i.e. someone who is, like Ernie, subject to the laws of nature) in a deterministic universe.
C. So, there is no possible universe in which deterministic laws obtain and a standard agent performs a free action.Footnote 20
Easy Fix is a valid argument, so it may appear that De Marco’s initial solution to the explanatory gap objection is a success.
Stepping back, however, grave problems with De Marco’s first solution become apparent. The reader will note that the terms ‘compatibility,’ ‘incompatibility,’ ‘incompossibility, ‘compatibilism,’ ‘incompatibilism,’ and ‘incompossibilism’ do not appear in any of the statements of the Zygote Argument we have considered so far, i.e. ZA-2006, ZA-2012, ZA-2013, ZA-2019, Simple Repair, and Easy Fix. As such, how one defines these terms is completely irrelevant to the validity of these arguments. By extension, how one defines the aforementioned terms is also irrelevant when assessing which of these manipulation arguments is vulnerable to an explanatory gap objection. It is irrelevant, then, that De Marco refers to the incompossibility thesis stated in the conclusion of Easy Fix by using the phrase “compatibilism is false” while I prefer the phrase “incompossibilism is true” (for reasons that I provide in Mickelson 2015a, 2017, 2019a, 2019b, and forthcoming). This means that we can safely set aside De Marco’s disapproval of my preferred labelling systemFootnote 21 and refocus on De Marco’s claim that Easy Fix constitutes a new solution to my explanatory gap objection to ZA-2012.
Once we focus on the content of De Marco’s Easy Fix, the differences between it and my Simple Repair disappear: the two arguments are constituted by the same three propositions presented in the same logical form. Simply put, Easy Fix and Simple Repair are the same argument.Footnote 22 It follows that De Marco’s first solution to the explanatory gap objection is a nonstarter.Footnote 23