John Locke

“ For simple ideas are all from things themselves, and of these the mind can have no more, nor other than what are suggested to it. It can have no other ideas of sensible qualities than what come from without by the senses ; nor any ideas of other kind of operations of a thinking substance, than what it finds in itself But when it has once got these simple ideas, it is not confined barely to observation, and what offers itself from without ; it can, by its own power, put together those ideas it has, and make new complex ones, which it never received so united. ”

“ This shows man’s power, and its ways of operation, to be much the same in the material and intellectual world. For the materials in both being such as he has no power over, either to make or destroy, all that man can do is either to unite them together, or to set them by one another, or wholly separate them. I shall here begin with the first of these in the consideration of complex ideas, and come to the other two in their due places. As simple ideas are observed to exist in several combinations united together, so the mind has a power to consider several of them united together as one idea ”

“ The abstrusest ideas we can have are all from two sources. If we trace the progress of our minds, and with attention observe how it repeats, adds together, and unites its simple ideas received from sensation or reflection, it will lead us further than at first perhaps we should have imagined. ”