From memory it is an easy step to what are called "ideas"--not in the Platonic sense, but in that of Locke, Berkeley and Hume, in which they are opposed to "impressions." You may be conscious of a friend either by seeing him or by "thinking" of him; and by "thought" you can be conscious of objects which cannot be seen, such as the human race, or physiology. "Thought" in the narrower sense is that form of consciousness which consists in "ideas" as opposed to impressions or mere memories. We may end our preliminary catalogue with BELIEF, by which I mean that way of being conscious which may be either true or false. We say that a man is "conscious of looking a fool," by which we mean that he believes he looks a fool, and is not mistaken in this belief. This is a different form of consciousness from any of the earlier ones. It is the form which gives "knowledge" in the strict sense, and also error. It is, at least apparently, more complex than our previous forms of consciousness; though we shall find that they are not so separable from it as they might appear to be. Besides ways of being conscious there are other things that would ordinarily be called "mental," such as desire and pleasure and pain. These raise problems of their own, which we shall reach in Lecture III. But the hardest problems are those that arise concerning ways of being "conscious." These ways, taken together, are called the "cognitive" elements in mind, and it is these that will occupy us most during the following lectures.