1. There is a story somewhere, of one that pretended to have been miraculously cured of blindness, wherewith he was born, by St. Alban or other St., at the town of St. Alban's; and that the Duke of Gloucester being there, to be satisfied of the truth of the miracle, asked the man, What colour is this? who, by answering, It is green, discovered himself, and was punished for a counterfeit: for though by his sight newly received he might distinguish between green, and red, and all other colours, as well as any that should interrogate him, yet he could not possibly know at first sight, which of them was called green, or red, or by other name. By this we may understand, there be two sorts of knowledge, whereof the one is nothing else but sense, or knowledge original (as I have said at the beginning of the second chapter), and remembrance of the same; the other is called science or knowledge of the truth of propositions, and how things are called, and is derived from understanding. Both of these sorts are but experience; the former being the experience of the effects of things that work upon us from without; and the latter the experience men have of the proper use of names in language.
And all experience being (as I have said) but remembrance, all knowledge is remembrance: and of the former, the register we keep in books, is called history. but the registers of the latter are called the sciences.
2. There are two things necessarily implied in this word knowledge; the one is truth, the other evidence; for what is not true, can never be known. For let a man say he knoweth a thing never so well, if the same shall afterwards appear to be false, he is driven to a confession, that it was not knowledge, but opinion. Likewise, if the truth be not evident, though a man holdeth it, yet is his knowledge of it no more than theirs that hold the contrary. For if truth were enough to make it knowledge, all truths were known: which is not so.
3. What truth is, hath been defined in the precedent chapter; what evidence is, I now set down. And it is the concomitance of a man's conception with the words that signify such conception in the act of ratiocination. For when a man reasoneth with his lips only, to which the mind suggesteth only the beginning, and followeth not the words of his mouth with the conceptions of his mind, out of a custom of so speaking; though he begin his ratiocination with true propositions, and proceed with perfect syllogisms, and thereby make always true conclusions; yet are not his conclusions evident to him, for want of the concomitance of conception with his words. For if the words alone were sufficient, a parrot might be taught as well to know a truth, as to speak it. Evidence is to truth, as the sap is to the tree, which so far as it creepeth along with the body and branches, keepeth them alive; when it forsaketh them, they die. For this evidence, which is meaning with our words, is the life of truth; without it truth is nothing worth.
4. Knowledge, therefore, which we call SCIENCE, I define to be evidence of truth, from some beginning or principle of sense.
