In Book I of his traditionally-titled Against the Logicians (Book VII of Adversus Mathematicos), Sextus Empiricus presents a critique of how past philosophers have attempted to define the human being. He notes that these philosophers would pass off a definition as an “explanation of man” (132), a strategy that, for Sextus, would surely fail.
First is the account that goes back to Aristotle, though Sextus does not cite him directly. He remarks that some philosophers define man as a “‘rational, mortal animal receptive of thought and knowledge’” (132). Sextus points out that this does not conjure up man himself, but rather lists of some of his attributes.
With respect to attributes, Sextus says that there are two distinct types, those which are “inseparable” (132) from the thing which has them and others which “can be separated” (132) from the attributed object. Those which cannot be separated from the object include its extended dimensions, for an extended body is inconceivable without such attributes. Separated attributes, for Sextus, include activities or potential activities which an individual can take part in. For instance, speaking and sitting are attributes of the human being, since these are things which “happen to” people, “but not continuously” (132).
However, as Sextus states, neither the separable nor the inseparable attributes are identical to the thing that bears them. Hence, the Aristotelian definition fails to define the human being, since it only recounts some of humankind’s attributes: that human beings are animals, an inseparable attribute, and that human beings possess the separable attributes of “‘reasoning’ and ‘possessing knowledge’” (133).
For Sextus, the other component of the given definition, that human beings are mortal, is not an attribute at all. He remarks that mortality is not something that is ever an attribute of a human being, since what makes a human seemingly mortal, death, is never a part of the human but something that happens after the human ceases to exist. One is never at the same time human and dead, hence, humans do not have mortality as an attribute in Sextus’ language.
Sextus also makes the point that none of these attributes uniquely give us the idea of the human being. For instance, being rational or possessing knowledge are also attributes of the gods, while many animals exist besides human beings. Of course, such a definition does not mean to imply that each of these attributes are uniquely true of humans, rather, it is “all of them in conjunction” that present the human being.
To this, Sextus asks how these various attributes can be united to produce the human without also “exceeding” or “falling short” (134) of what human beings are. After all, human beings are not at all times rational or in possession of knowledge, nor do they possess mortality as an attribute because “death is not yet present” (134). So in this case, listing all of these attributes at any time may exclude some human beings, namely those who are not currently reasoning, possessing knowledge, or even simply still living. Hence, this definition exceeds that of human beings. Similarly, these are not the only attributes of human beings, so the definition in another sense falls short of producing the human.
The definition of man from Platonic sources also falls under Sextus’ scrutiny. He says that this definition describes man as a “‘featherless, two-footed, flat-nailed animal, receptive of political science’” (134). Such a definition fails to capture the human being for the same reasons as the Aristotelian one, namely that it gives a list of attributes, some of which are not constant in humans. Further, Sextus calls this definition “even worse than the others” (134) because it contains some negative attributes, such as ‘featherless’, along with positive ones, such as ‘twofooted’. That is, some of what is in this definitions are not attributes of humans, but an account of what are not human attributes.
Since no definition like those given can accurately capture the idea of human beings, or produce the “conception of particular men” (132), Sextus concludes that it is impossible to properly define the human being. Humans are, hence, left without a proper conception of themselves.
Sextus Empiricus. Selections from the Major Writings on Scepticism, Man, & God. Ed. Philip P. Hallie. Trans. Sanford G. Etheridge. Indianapolis, IN: Hackett, 1985. pp. 132-134.