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There was a time when medical men entertained so determined' a dislike to the word theory, that they could scarcely tolerate the term. If any such remain, I would heg them to reflect that hypothesis and theory are the natural and inevi: table result of thinking; so that if they refuse to allow of any theory, they must prohibit all thought.
The antipathy which some have entertained to the term theory, has arisen from its misapplication. For opinions drawn from very partial views of subjects, sometimes having no foundation on facts; opinions formed by processes of mind, similar to those which occur in dreaming, when lawless imagination produces combinations and associations without any reference to realities; opinions, as unlike what I should understand by theory as darkness is to light,
to light, have nevertheless
been often proposed as theories and so denominated. That such foolish speculations, such „waking dreams, will mislead and deceive us, cannot be doubted ; and hence has arisen the prejudice which some have entertained against the term.
The greatest philosophers were through the whole course of their enquiries and demonstrations, theorists. Theorizing, according to my conception of the word, means nothing more than thinking correctly, in a concatenated manner, and in conformity to rules which I shall presently have occasion to notice. It is scarcely necessary for me to assert that this kind of thinking is useful, and promotive of Science. For was it not thinking in this manner on the cause of an apple falling from a tree, that led Sir Isaac Newton to ascertain the laws of attracțion? was it not thinking thus which led him
to perceive that the operation of the same causes might perpetuate the regular motions of the planetary system? Why do we note facts with accuracy, or collect them with diligence? why do we interrogate nature by experiment? Is it not because we wish to prove some of our own opinions to be true, or the opposing opinions of others to be false ? or, because we wish to enlarge the boundaries of science in a direction in which we think they admit of extension? What induces one person to prohibit another from theorizing? Is it not because he has himself attempted it in vain, and therefore deems the attempt unavailing ?
Feelings and opinions are the chief sources of all our intellectual conduct: we ought therefore to cultivate good and how norable feelings, and to scrutinize opinions, with a view to entertain none but those
that appear correct; and such an examina . tion, to which I now invite you, must be allowed to be a proper exercise of intellect.
Since thinking is inevitable, our chief enquiry should be how we ought to. think or theorize; and on this point Newton himself has condescended to instruct us. Our theories, hypotheses, or opinions, for to me all these words seem to refer to one and the same act of the mind-should be verifiable or probable, and should rationally account for all the known phænomena of the subject they pretend to explain; under which circumstances it is allowable to maintain them as good, until others more satisfactory be discovered. No man who, thus theorizes need feel shame in this employment of his intellec tual powers; no man can feel arrogance, for it is acknowledged that his theory is but a probable and rational conjecture,
Besides, we never can be sure, that the series of facts belonging to any subject is full or complete; new ones may be discovered, that would overturn our best established theories.
Upon the foregoing terms alone do I wish to uphold Mr. Hunter's theory of life; and I do so on the present occasion, because it seems highly probable, it was his thinking in the manner he was known to do, that caused him to survey all the facts connected with the subject of life in general with so much accuracy, as well as to note 'its disordered states and sympathies in a manner which has so greatly contributed to increase our practical knowledge. It is highly probable that it was his hypothesis "respecting life which incited him to enquiries by which he has been able to supply the deficient facts, so as to establish his conjectures, or convert his hypothesis into a theory.