You next distinguish ideas (by which you mean thoughts in so far as they are like images) into three classes: innate, adventitious and made up. In the first class you put ‘your understanding of what a thing is, what truth is and what thought is’. In the second class you put ‘your hearing a noise, seeing the sun and feeling a fire’. And in the third class you put ‘your invented idea of sirens and hippogriffs’. You add that all your ideas may perhaps be adventitious or they may all be innate or all made up, since you have not as yet clearly perceived their origin. But in case some fallacy should creep in before you have managed to perceive the origin of your ideas, I should like to go further and note that all ideas seem to be adventitious – to proceed from things which exist outside the mind and come under one of our senses. The mind has the faculty (or rather is itself the faculty) of perceiving adventitious ideas – those which it receives through the senses and which are transmitted by things; these ideas, I say, are quite unadorned and distinct, and are received just exactly as they are. But in addition to this, the mind has the faculty of putting these ideas together and separating them in various ways, of enlarging them and diminishing them, of comparing them, and so on.