a. First, we observe the mind by the mind. It would seem therefore that we are always in danger of leaving out the half of that which is the subject of our enquiry. We come at once upon the difficulty of what is the meaning of the word. Does it differ as subject and object in the same manner? Can we suppose one set of feelings or one part of the mind to interpret another? Is the introspecting thought the same with the thought which is introspected? Has the mind the power of surveying its whole domain at one and the same time?--No more than the eye can take in the whole human body at a glance. Yet there may be a glimpse round the corner, or a thought transferred in a moment from one point of view to another, which enables us to see nearly the whole, if not at once, at any rate in succession. Such glimpses will hardly enable us to contemplate from within the mind in its true proportions. Hence the firmer ground of Psychology is not the consciousness of inward feelings but the observation of external actions, being the actions not only of ourselves, but of the innumerable persons whom we come across in life. b. The error of supposing partial or occasional explanation of mental phenomena to be the only or complete ones. For example, we are disinclined to admit of the spontaneity or discontinuity of the mind--it seems to us like an effect without a cause, and therefore we suppose the train of our thoughts to be always called up by association. Yet it is probable, or indeed certain, that of many mental phenomena there are no mental antecedents, but only bodily ones. c. The false influence of language. We are apt to suppose that when there are two or more words describing faculties or processes of the mind, there are real differences corresponding to them. But this is not the case. Nor can we determine how far they do or do not exist, or by what degree or kind of difference they are distinguished. The same remark may be made about figures of speech. They fill up the vacancy of knowledge; they are to the mind what too much colour is to the eye; but the truth is rather concealed than revealed by them. d. The uncertain meaning of terms, such as Consciousness, Conscience, Will, Law, Knowledge, Internal and External Sense; these, in the language of Plato, 'we shamelessly use, without ever having taken the pains to analyze them.' e. A science such as Psychology is not merely an hypothesis, but an hypothesis which, unlike the hypotheses of Physics, can never be verified. It rests only on the general impressions of mankind, and there is little or no hope of adding in any considerable degree to our stock of mental facts. f. The parallelism of the Physical Sciences, which leads us to analyze the mind on the analogy of the body, and so to reduce mental operations to the level of bodily ones, or to confound one with the other.