John Stuart Mill: The existence of ‘other’ minds.

“By what evidence do I know, or by what considerations am I led to believe, that there exist other sentient creatures; that the walking and speaking figures, which I see and hear, have sensations and thoughts, or in other words, possess Minds?  . . .

first, they have bodies like me, which I know to be the antecedent condition of feelings …

secondly, they exhibit the acts and other outward signs, which in my own case I know by experience to be caused by feelings.

I am conscious in myself of a series of facts connected by a uniform sequence, of which the beginning is modifications of my body, the middle is feelings, the end is outward demeanor.   In the case of other human beings I have the evidence of my senses for the first and last links of the series, but not for the intermediate link.

I find, however, that the sequence between the first and last is as regular and constant in those other cases as it is in mine.   In my own case I know that the first link produces the last through the intermediate link, and could not produce it without.

Experience, therefore, obliges me to conclude that there must be an intermediate link; which must either be the same in others as in myself, or a different one: I must either believe them to be alive or to be automatons: and by believing them to be alive, that is, by supposing the link to be of the same nature as in the case of which I have experience, and which is in all other respects similar, I bring other human beings, as phenomena, under the same generalizations, which I know by experience to be the true theory of my own existence.”

John Stuart Mill, An Examination of Sir William Hamilton’s Philosophy, 1865.  Cited from the Introductory Quotes to the first chapter of Nicholas Humphrey, Consciousness Regained: Chapters in the Development of Mind, Oxford, 1983.