There are certain occurrences which we are in the habit of calling "mental." Among these we may take as typical BELIEVING and DESIRING. The exact definition of the word "mental" will, I hope, emerge as the lectures proceed; for the present, I shall mean by it whatever occurrences would commonly be called mental. I wish in these lectures to analyse as fully as I can what it is that really takes place when we, e.g. believe or desire. In this first lecture I shall be concerned to refute a theory which is widely held, and which I formerly held myself: the theory that the essence of everything mental is a certain quite peculiar something called "consciousness," conceived either as a relation to objects, or as a pervading quality of psychical phenomena. The reasons which I shall give against this theory will be mainly derived from previous authors. There are two sorts of reasons, which will divide my lecture into two parts: (1) Direct reasons, derived from analysis and its difficulties; (2) Indirect reasons, derived from observation of animals (comparative psychology) and of the insane and hysterical (psycho-analysis).