John Locke

“ Upon this ground it is, that particular demonstrations in mathematics afford general knowledge. If then the perception, that the same ideas will eternally have the same habitudes and relations, be not a sufficient ground of knowledge, there could be no knowledge of general propositions in mathematics ; for no mathematical demonstration would be any other than particular : and when a man had demonstrated any proposition concerning one triangle or circle, his knowledge would not reach beyond that particular diagram. ”

“ This, I think, one may call habitual knowledge. And thus a man may be said to know all those truths which are lodged in his memory, by a foregoing clear and full perception, whereof the mind is assured past doubt as often as it has occasion to reflect on them. ”

“ But yet it is evident the author himself knows the proposition to be true, remembering he once saw the connexion of those ideas ; as certainly as he knows such a man wounded another, remembering that he saw him run him through. But because the memory is not always so clear as actual perception, and does in all men more or less decay in length of time, this, amongst other differences, is one which shows that demonstrative knowledge is much more imperfect than intuitive, as we shall see in the following chapter. ”

“ Such a memory as that, able to retain such a train of particulars, may be well thought beyond the reach of human faculties, when the very discovery, perception, and laying together that wonderful connexion of ideas, is found to surpass most readers’ comprehension. ”

“ In his adherence to a truth, where the demonstration by which it was at first known is forgot, though a man may be thought rather to believe his memory than really to know, and this way of entertaining a truth seemed formerly to me like something between opinion and knowledge ”

“ Thus, « blue is not yellow, » is of identity. « Two triangles upon equal bases between two parallels are equal, » is of relation. « Iron is susceptible of magnetical impressions, » is of co-existence. « God is, » is of real existence. ”