These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.
3.

The Objects of Sensation one Source of Ideas First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them.

And thus we come by those IDEAS we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions.

This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call SENSATION.
4.

The Operations of our Minds, the other Source of them.
Secondly, the other fountain from which experience furnisheth the understanding with ideas is,--the perception of the operations of our own mind within us, as it is employed about the ideas it has got;--which operations, when the soul comes to reflect on and consider, do furnish the understanding with another set of ideas, which could not be had from things without.