John Locke: An Essay Concerning Human Understanding: Book 2: Chapter 6

Book II - Chapter VI
Of Simple Ideas of Reflection

1. Simple ideas are the operations of mind about its other ideas. The mind receiving the ideas mentioned in the foregoing chapters from without, when it turns its view inward upon itself, and observes its own actions about those ideas it has, takes from thence other ideas, which are as capable to be the objects of its contemplation as any of those it received from foreign things.

 2. The idea of perception, and idea of willing, we have from reflection. The two great and principal actions of the mind, which are most frequently considered, and which are so frequent that every one that pleases may take notice of them in himself, are these two:- 

           Perception, or Thinking; and
           Volition, or Willing.
The power of thinking is called the Understanding, and the power of volition is called the Will; and these two powers or abilities in the mind are denominated faculties.

 Of some of the modes of these simple ideas of reflection, such as are remembrance, discerning, reasoning, judging, knowledge, faith, &c., I shall have occasion to speak hereafter.