J/AMES G/REGORY, the third of this name, was the son and the successor in the chair of medicine in Edinburgh of John Gregory.He was born in Aberdeen in 1753, and died in 1821.For many years lie stood at the head of his profession as a physician in Edinburgh.He published a number of medical works.His " Conspectus Medicinae Theoreticae,"written in good Latin, was long used as one of the works on which the candidates for medical degrees were examined.He comes before us as author of " Philosophical and Literary Essays," dated Jan.1St, 1790, and published 1792.He dedicates the work to Reid, and acknowledges that lie had taken a principal argument from one of Reid's observations in the essays on the " Intellectual Powers of Man." The most important essay is " On the difference between the Relation of Motive and Action and that of Cause in Physics, on Physical and Mathematical Principles." In an introduction in which he is long in coming to the point, he dwells on the looseness and ambiguity of the word "cause," and remarks that if" there should be occasion to attend to the more minute or specific differences among the several things comprehended under the genus 'cause,' it would be highly expedient or rather absolutely necessary to give to each of them a specific name, were it only an addition to the generic name cause." He has a glimpse of there being more than one agent involved in cause."No substance is of itself a physical cause; this depends on its relation to some other substance, and implies the tendency to change in the latter." " The substance in which the change is observed is considered as the subject, the other as the cause; and as change occurs generally in both or all of the substances so related, though it be not always of the same kind in them all, it depends on the circumstance of our attention being directed first and chiefly to one or other of them, and on our opportunities of observing the changes that occur in them, which of them we shall regard as the subject and which as the cause, as in the example of the communication and the loss of motion, of mutual gravitation, of the solution of salt and saturation of water, the melting of ice, or the boiling of water and the absorption of heat." This is a vague anticipation of the doctrine started in our day as to their being two or more agents in all material causation, --a doctrine, I may add, not yet followed out to its consequences in regard to mechanical, chemical, and physiological action.He insists that there is in mind a certain independent self-governing power which there is not in body; in consequence of which there is a great difference between the relation of motive and action and that of cause {265} and effect in physics; and by means of which a person in all cases may at his own discretion act, either according to or in opposition to any motive or combination of motives applied to him; while body in all cases irresistible undergoes the change corresponding to the cause or combination of causes applied to it." I propose to demonstrate the falsity and absurdity of the doctrine of necessity on mathematical principles, in mathematical form, partly by means of algebraic formulae, partly with the help of diagrams," and he uses mathematical formulae and others invented by himself.He endeavors to show by an indirect demonstration that the doctrine of necessity must be false, as it leads to false conclusions.He takes the case of a porter carrying a burden: " If a guinea should be offered for carrying it in the direction of A B, and half a guinea for carrying it in the direction A C, and let him be assured that if lie can earn the guinea he cannot earn the half guinea, and that if he earn the half guinea he cannot earn the guinea; will he go in the direction of A B or A C, or remain at rest in A? " He answers, that if the principle on which the necessity is founded be true, he must move in the diagonal A D." But as it must be acknowledged that the porter will not move in that direction, experience proving the fact, then it follows that the law of physical causes and that of motives do not coincide, and that the relation between motives and actions is not necessary as between physical causes and their effects." Dr.Crombie attacked Dr.
Gregory's reasoning, Sir W.Hamilton says "with much acrimony and considerable acuteness." There subsequently appeared letters from Dr.James Gregory, of Edinburgh, in defence of his essay on the " Difference of the Relation between Motive and Action and that of Cause and Effect in Physics; with Replies by the Rev.Alexander Crombie, LL.D."London: 1819." It is much to be regretted that Dr.Gregory did not find leisure to complete his answer to Messrs Crombie, Priestley, and Co., of which five hundred and twelve pages have been printed, but are still unpublished."(Coll.Works of Reid, by Hamilton.p.87.) We are reminded that the clearest defence by Reid of the doctrine of the ******* of the will is contained in letters to Dr.Gregory, and published in Hamilton's edition of his works.At a time when the Calvinistic faith of Scotland might have led theologians into perilous necessarian doctrines, it was of great moment to have the essential liberty of will (which Calvin never denied) defended by such philosophers as Reid and Gregory.
