6. Chap. III.--Objection answered.

"Whence then comes our capacity of conceiving in thought things which we have never seen?" What, think you, can be the cause of this, but a certain faculty of diminution and addition which is innate in the mind, and which it cannot but carry with it whithersoever it turns (a faculty which may be observed especially in relation to numbers)? By the exercise of this faculty, if the image of a crow, for example, which is very familiar to the eye, be set before the eye of the mind, as it were, it may be brought, by the taking away of some features and the addition of others, to almost any image such as never was seen by the eye. By this faculty also it comes to pass, that when men's minds habitually ponder such things, figures of this kind force their way as it were unbidden into their thoughts. Therefore it is possible for the mind, by taking away, as has been said, some things from objects which the senses have brought within its knowledge, and by adding some things, to produce in the exercise of imagination that which, as a whole, was never within the observation of any of the senses; but the parts of it had all been within such observation, though found in a variety of different things: e.g., when we were boys, born and brought up in an inland district, we could already form some idea of the sea, after we had seen water even in a small cup; but the flavour of strawberries and of cherries could in no wise enter our conceptions before we tasted these fruits in Italy. Hence it is also, that those who have been born blind know not what to answer when they are asked about light and colours. For those who have never perceived coloured objects by the senses are not capable of having the images of such objects in the mind.