Self-knowledge can be considered a topic that is brought up very subtly in De Anima. Aristotle certainly questions the definition of the soul of living beings, but does so through methods observation. Observing one’s senses certainly requires self-inquiry in order to obtain self-knowledge but usually, this form of inquiry transforms into a rather spiritual-like type of self-knowledge, instead of a more observational type of self-knowledge—which Aristotle’s inquiries resemble more closely. The reason why Aristotle’s inquires about self-knowledge are more observational rather than spiritual, can be explained by his profound interest in biology which is much more “actual” as apposed to other forms of inquiry that are “potential”.

Inquiring about the senses is perhaps an area that has the most potential for self-knowledge since it requires one to question his own senses rather than making observations about the way other living beings sense. Aristotle’s Book III in the section of De Anima deals more with self-knowledge compared to any of the other sections, since the inquiries require one’s self-toughness. Aristotle makes an interesting observation about thinking and understanding considering them to be senses just like sight or smell. However, thinking can be a very deceptive sense since it encompasses the capability to consider something not right. Animals and plants perceive everything as right—as is; while thought makes humans to question this right trueness of something perceived, and transform it into falseness. In Aristotle’s terms, this is rather a deceptive ability of intellect, rather than an evolutionary one.

Nevertheless, the ability to consider something false rather than considering everything perceivable to be always true, is what allows a being with such a capacity to inquire about self-knowledge. Self-knowledge is something that only intellect is capable of achieving and according to Aristotle, animals are not capable of considering something false and therefore cannot inquire about self-knowledge.