This was probably my favorite chapter so far, given my chosen craft. I continue to be amazed at Hobbes's literalism. He rails against metaphor and insists that words, and the training together of words, have precise meaning. Hobbes is pursuing truth. Words are his tools. Should his words be erroneous, he might find himself as the scientist fumbling with scales out of calibration. (TNC and The Horde are jacking for beats.) 

First, when men register their thoughts wrong by the inconstancy of the signification of their words; by which they register for their conceptions that which they never conceived, and so deceive themselves. Secondly, when they use words metaphorically; that is, in other sense than that they are ordained for, and thereby deceive others. Thirdly, when by words they declare that to be their will which is not. Fourthly, when they use them to grieve one another: for seeing nature hath armed living creatures, some with teeth, some with horns, and some with hands, to grieve an enemy, it is but an abuse of speech to grieve him with the tongue, unless it be one whom we are obliged to govern; and then it is not to grieve, but to correct and amend.

By this it appears how necessary it is for any man that aspires to true knowledge to examine the definitions of former authors; and either to correct them, where they are negligently set down, or to make them himself. For the errors of definitions multiply themselves, according as the reckoning proceeds, and lead men into absurdities, which at last they see, but cannot avoid, without reckoning anew from the beginning; in which lies the foundation of their errors. From whence it happens that they which trust to books do as they that cast up many little sums into a greater, without considering whether those little sums were rightly cast up or not; and at last finding the error visible, and not mistrusting their first grounds, know not which way to clear themselves, spend time in fluttering over their books; as birds that entering by the chimney, and finding themselves enclosed in a chamber, flutter at the false light of a glass window, for want of wit to consider which way they came in. 

So that in the right definition of names lies the first use of speech; which is the acquisition of science: and in wrong, or no definitions, lies the first abuse; from which proceed all false and senseless tenets; which make those men that take their instruction from the authority of books, and not from their own meditation, to be as much below the condition of ignorant men as men endued with true science are above it. For between true science and erroneous doctrines, ignorance is in the middle. Natural sense and imagination are not subject to absurdity. Nature itself cannot err: and as men abound in copiousness of language; so they become more wise, or more mad, than ordinary. Nor is it possible without letters for any man to become either excellently wise or (unless his memory be hurt by disease, or ill constitution of organs) excellently foolish. For words are wise men's counters; they do but reckon by them: but they are the money of fools, that value them by the authority of an Aristotle, a Cicero, or a Thomas, or any other doctor whatsoever, if but a man.