In a passage in the Treatise on the Emendation of the Intellect, Spinoza claims that, under certain circumstances, some individuals "must be regarded as automata, completely lacking a mind" (TIE, 48; Curley 1985, 22). Examples that employ soulless automata (mostly referred to as “zombies”) are commonly used in contemporary philosophy of mind. There, zombies are conceived of as beings virtually identical to their conscious counterparts in every aspect of their behaviour and relevant physical functions, "but lacking conscious experiences altogether" (Chalmers 1996, 94).

However, Spinoza’s soulless automata differ in (at least) two respects: (1) there’s a specific kind of behaviour that gives such zombies or soulless automata away and (2) they are not fictional, philosophically useful entities, but real people—the sceptics. So, what is Spinoza after with this analogy?

 Let’s look at how Spinoza describes the sceptic-automaton analogy (TIE 47, Curley 1985, 22):

Perhaps, afterwards, some sceptic would still doubt both the first truth itself and everything we shall deduce according to the standard of the first truth. If so, then either he will speak contrary to his own consciousness, or we shall confess that there are men whose minds also are completely blinded, either from birth, or from prejudices, i.e., because of some external chance. For they are not even aware of themselves. […] If they affirm or doubt something, they do not know that they affirm or doubt. They say that they know nothing, and that they do not even know that they know nothing. And even this they do not say absolutely. For they are afraid to confess that they exist, so long as they know nothing. In the end, they must be speechless, lest by chance they assume something that might smell of truth.

Not granting awareness to anyone convinced by radical scepticism seems pretty extreme. So, what is Spinoza’s way out? He considers two possibilities: sceptics are either liars or automata. In the first scenario, the words of sceptics do not depict the truth: their assertions systematically fail to describe any of their actual beliefs (anything they may take themselves to know or not to know, about themselves, the world, etc.). Such sceptics are certainly conceived of as human beings, with a human soul and conscious access to at least some of their mental states. However, they are determined to lie whenever they are asked about what they know or seem to know.

In the second scenario, sceptics are “men whose minds are completely blinded.” Spinoza uses ‘blinded’ here as a metaphor for lack of self-awareness. Let this sink in: sceptics have no awareness of what is going inside or outside themselves– the words they utter have no meaning, and as far as we may know, they could just as well be attributed to a machine. In both cases, the conclusion is the same, "there is no speaking of the sciences with them" (TIE 48; Curley 1985, 22). Yet, the second claim—that such sceptics may really be conceived as soulless automata—sounds a bit exaggerated, if not implausible.

And yet, for Spinoza, there seems to be nothing wrong in being counted as an "automaton." Here are a couple of reasons why. To begin with, one of the explicit purposes of the Treatise is to conceive of the human soul "as acting according to certain laws, like a spiritual automaton" (TIE 85; Curley 1985, 37). And such a goal squares well with some of Spinoza’s metaphysical cornerstones (such as his rejection of free will and his mind-body parallelism), which demand that anything concerning bodies and physical objects be conceived in rigorously mechanistic terms, through the laws of physics alone. If so, then this consideration must also concern all functions and possible ways of behaving that we may observe in and ascribe to a human body: they should, in principle, be explainable by considering the nature of the human body alone, excluding any reference to mental states. A well-performing human body, one that we would associate with a well-performing human mind (that is, with a corresponding spiritual automaton) and its relevant conscious experience, is properly understood as a well-performing corporeal automaton. Seen from this perspective, as Spinoza clarifies, there is not much difference between radical sceptics and us. Of course, we might say: sceptics are humans, aren’t they? And, as humans, they are forced to have normal human behaviour, to strive for the same things we strive for, and to display a reasoned use of language, aimed at satisfying the needs of their physiological nature (TIE 48; Curley 1985, 22):

For as far as the needs of life and society are concerned, necessity forces them to suppose that they exist, and to seek their own advantage, and in taking oaths, to affirm and deny many things.

This is the kind of behaviour we would attribute to, and expect from, any human being. In such occasions, in Spinoza’s account, we do not fail to regard at similar individuals as humans, and to ascribe them a human soul—a soul, that is to say, that is capable of all the functions of which your soul or mine is also capable. In real life, we sympathise with them and imitate or share their affects.

And yet, we should not forget that, despite all these commonalities between humans and radical sceptics, Spinoza concludes his anti-sceptic rant in a different way: he invites us to regard these individuals as "automata, completely lacking a mind." Perhaps this conclusion is intended to respond to the sceptic’s stubbornness and to how such stubbornness makes engagement in meaningful philosophical discussion impossible. Perhaps! But, even so, it does it by suggesting one thing: if we judge the sceptics through their words alone, we would ultimately have no criteria to assess whether we are interacting with self-aware human beings, or with some other sort of automatic device. As far as we may infer from what these sceptics say, they could either have some access to their mental content, albeit in a way that is totally unrecognisable to humans (it would be of a radically different kind, as for an alien, or a bat ([recall Nagel 1974]) or have no conscious access to their mental states at all.

Here’s a little addendum. I wonder whether the way Spinoza treats the case of the sceptics could also be dictated by a deeper concern, involving his apparently uncompromising take on deceptive behaviour in general, and on lying in particular, and the evil consequences that they may cause in terms of divisions and conflicts between individuals (Ethics IV, prop.72; Curley 1985, 586–7). Spinoza seems willing to admit that I can form relationships of friendship with other humans also because of my capacity to acknowledge, in other individuals, a kind of subjective experience like my own (should I find myself in similar circumstances, that is). If I have reasons to believe that other individuals may share with me the same nature, then I must also ascribe them a similar way of being aware of their mental states, beliefs, attitudes and, most importantly, a similar experience of what I feel as joy, sadness, and desire in general.

Deceptive behaviour and lies, for Spinoza, seem instead to have an opposite effect in us. They can make the subjective experience of another individual appear different and alien from mine, impenetrable and mysterious, by concealing one’s own real beliefs and intentions, and turning the words used to describe them into meaningless sounds. Taken in this sense, Spinoza’s use of the notion of a soulless automaton in the context of the radical sceptics also works as a reminder of some of the worst consequences that may follow, in his account, should one be challenged with systematic deceptive behaviour. As far as deception represents an obstacle to recognising similarities in our ways of experiencing the world, it threatens and hinders our capability to empathise and create stable relationships with other human beings, so much so that it can bring us to the point of shattering the reasons we have for believing that someone else may also have the capacity to perceive and feel the same things that we perceive and feel.  

Acknowledgements: I thank Laura Georgescu for her insightful suggestions and editorial assistance