This order of our external feelings comprehends all those _states_ of mind, however various they may be, which immediately succeed the changes of state, produced, in any of our organs of sense, by the presence of certain external bodies. The mental affections are themselves,--as I have said,--commonly termed _sensations_; but we have no verb, in our language, which exactly denotes what is expressed in the substantive noun. To _feel_ is, in its two senses, either much more limited or much more general, being confined, in its restricted meaning, to the sensations of one organ, that of touch,--and as a more general word, being applicable to all the varieties of our consciousness, as much as to those particular varieties, which are immediately successive to the affections of our organs of sense. We are said, in this wider use of the term, to feel indignation, love, surprise, as readily as we are said to feel the warmth of a fire, or the coldness of snow. In defining our sensations, to be those mental affections, which are immediately successive to certain organic affections, produced by the action of external things, it is very evident, that I have made two assumptions,--first of the existence of external things, that affect our organs of sense; and, secondly of organs of sense, that are affected by external things;--unless, indeed, the assumption of the existence of organs of sense be considered,--as in philosophic truth it unquestionably is--only another form of the assumption of the existence of external things, since, in relation to the sentient mind, the organs thus supposed to exist, are, in strictness of language, _external_, as much as the objects supposed to act upon them. All of which we are truly conscious, in sensation, is the mental affection, the last link of the series, in the supposed process; what we term our perceptions of organs of sense, or of other external things that act upon these--our ideas, for example, of a brain or an eye, a house or a mountain, being as truly states of our own percipient mind, and nothing but states of our own mind, as our feeling of joy or sorrow, hope or fear, love or hate,--to which we never think of giving an _existence_, nor a direct and immediate _cause_ of existence, _out_ of ourselves. By the very constitution of our nature, however, or by the influence of associations as irresistible as intuition itself,--it is impossible for us not to feel this essential reality in the causes of one set of our mental affections, in the same manner as it is impossible for us to ascribe it to another set. The brain, the eye, the house, the mountain, we believe, and cannot but believe, to have external existence, independent of our own; the joy and sorrow, hope and fear, love and hate, we believe, and cannot but believe, to be merely states of our own mind, occasioned by other former states of mind, and dependent, therefore, for their continuance, on our own continued existence only.