And though by men's actions we do discover their design sometimes; yet to do it without comparing them with our own, and distinguishing all circumstances by which the case may come to be altered, is to decipher without a key, and be for the most part deceived, by too much trust or by too much diffidence, as he that reads is himself a good or evil man.--Hobbes (1651) Leviathan, Introduction
In the introduction to the Leviathan, Hobbes informs the reader that by reading his book one can learn one of the hardest skills, "harder than to learn any language or science," that is to read in oneself, not any particular other individual, "but mankind." This skill of abstraction (or the ability to discern a universal) is necessary in order to be a succesful political ruler ("governor of a whole nation"). Hobbes implies, thus, that he can teach political virtue.* It is an open question if this skill is also sufficient for political virtue. For, Hobbes leaves no doubt that he does not just think he has he ability to teach the skill but also that he possesses it too; it is not at all obvious that he is a ruler or wishes to be one.
As aside, it is often thought that an absolute ruler would welcome Leviathan, but this is not obvious. For, while some rulers may wish to have a work available that may seem to justiy their and, perhaps, perfects their rule, other rulers might be alarmed to learn that an author claims to teach the skill that could improve (that is, to displace) them.
Hobbes suggests there are two natural cognitive fallacies that prevent the skill of abstraction from operating reliably. First, our causal inferences from effects (visible actions and utterances) to causes (passion driven intentions) are unreliable. Hobbes offers two reasons for this: (i) our inferences our unreliable not just because people's presentations may mask intentions.** They are also unreliable because (ii) the very same passions in different people can be oriented toward dramatically different objects. In fact, Hobbes offers two reasons for (ii): (ia) variation in people's education and (ib) what he calls "constitution individual," that is, our individual material organization. Thus, Hobbes thinks that standardizing education and standardizing the human form might increase the reliability of our inferences about each other. Cheating a bit: we may say that in Leviathan Hobbes promotes the former option while his mentor, Bacon, promotes the latter (in New Atlantis). Second, we have a natural tendency to project features of our own character onto our interpretations of others thereby our ordinary interpretations are ultimately most revealing about ourselves (rather than disclose others and -- because Hobbes systematically switches between decoding people and reading texts -- books). Both ordinary, cognitive fallacies generate, we may say, the wrong 'imputs' from which we abstract. (Garbage in, garbage out.) In particular, they prevent us from discerning key, if not all, causal factors ("distinguishing all circumstances by which the case may come to be altered").
So, Hobbes's task as teacher of political virtue, or the art of ruling, presupposes that he can help his student/reader (a) recognize, and, perhaps, disable these cognitive fallacies and (b) teach the art of dissecting relevant causal factors (passions) that animate human life. In so far as he implies that the human form is just a material machine, it seems that with (a-b) in place to say that the definition, or essence, of the universal, humankind, is a complicated causal formala (with weights, enabling conditions, etc.).
One final thought. Hobbes insists that decoding people and texts is naturally very difficult. So, he ought to expect lots of misinterpretations of his work. Yet, he claims to have made it (relatively) easy for his reader by his mode of presentation ("orderly and perspicuously"). That mode of presentation also has to teach the art of decoding reliably in the unfolding text itself, unless Hobbes thinks that some just are naturally more skilled at code-breaking (see here and here).
*I avoid 'political science,' not of fear of anachronism nor in order to set it apart from Hobbes' contrastive use of 'science,' but because post Max Weber, we tend not to associate political science (nor political philosophy) with the art of ruling as such.
**Given the emphasis that Hobbes places on this -- both in placeement, right at the start of the book, as well as in rhetoric "dissembling, lying, counterfeiting, and erroneous doctrines," -- it is, of course, worth asking to what degree a reader can infer Hobbes's intentions from his presentation.