‘By our senses and our memory, by testimony and other means, we have the certain knowledge of many truths which we do not perceive to be necessary; their contraries therefore may be possible for aught we know. But we know that whatever is true, whether necessary or not, is possible. Our knowledge therefore of what is possible keeps pace with our knowledge of truth, whether contingent or necessary. Beyond this, I am afraid our knowledge of what is possible is conjectural. And although we are apt to think everything to be possible which we do not perceive to be impossible, yet in this we may be greatly deceived. You know well, sir, that mathematics affords many instances of impossibilities in the nature of things, which no man would have dreamed of or believed, until they were discovered by accurate and subtle reasoning. Perhaps if we were able to reason demonstratively to as great an extent in other subjects as in mathematics, we might discover many things to be impossible which we now take to be possible. We are apt to think it possible that God might have made an universe of sensible and rational creatures, into which neither natural nor moral Evil should ever enter. It may be so for what I know. But how are you certain that this is possible? I can distinctly conceive it, say you; therefore it is possible. I do not admit this argument. May not a man who is a mathematician as distinctly conceive that in the infinite variety of numbers gradually ascending, there is no ratio whatsoever which is not equal to the ratio of some one whole number to some other whole number? Yet the mathematician can demonstrate that there are innumerable ratios which are not equal to the ratio of some one number to another. Many mathematicians, taking it for granted that it was possible to square the circle, have spent their lives in a fruitless pursuit. May not our taking things to be possible, in matters of higher moment, when we can show no good reason that they are so, lead us into unnecessary disputes and vain theories? Ought we to admit that as a just argument in reasoning, or even as a pressing difficulty, which is grounded on the supposition that such a thing is possible, when in reality we have no good evidence of its being possible, and for anything we can show to the contrary, it may be impossible?’
A letter to Dr. Gregory in March 1786 shows the Essays on the Active or Moral Powers in the press:—‘I am proud of the approbation you express of the Essays. I have made some corrections and additions, but such as I hope will not make it necessary to write the book over again. But I wish, if I find health and leisure in summer, to add some Essays to go before that on “Liberty of the Will,” in order to give some further elucidation of the principles of morals. I expect your remarks and D. Stewart’s on what is in hand. It will be no inconvenience to wait two, three, or even four months.’ Two years later, early in 1788, when he was in his seventy-eighth year, the five Essays on the Active Powers of Man were published. This was Reid’s last appearance as a philosophical author. The eight Essays of 1785, and the five Essays of 1788, all relate to human Power—power immanent or intellectual, and power overtly operative or moral.
In March, a few weeks after the book appeared, Beattie writes to Sir W. Forbes:—
‘I have been looking into Dr. Reid’s book on The Active Powers of Man. It is written with his usual perspicuity and acuteness; is in some parts very entertaining; and to me, who have been obliged to think much on those subjects, is very interesting throughout. The question concerning Liberty and Necessity [of the Will] is very fully discussed, and very ably, and I think nothing more need be said about it. I could have wished that he had given a fuller examination of the passions, and been a little more practical in illustrating the duties of morality. But his manner in all his writings more turned to speculative than to practical philosophy; which may be owing to his having employed himself so much in the study of Locke, Hume, Berkeley, and other theorists; and partly, no doubt, to the habits of study and modes of conversation which were fashionable in this country in his younger days. If I were not personally acquainted with the Doctor, I should conclude from his books that he was rather too warm an admirer of Mr. Hume. He confutes, it is true, some of his opinions; but pays them much more respect than they are entitled to.’
To Beattie’s less profound intelligence, indignant sentiment was more acceptable, in defence of fundamental faith, than the calm inquiry and sympathetic criticism of Reid.
The Literary Society which met monthly in the College was occasionally a channel for his thoughts through all the years of the Glasgow professorship, as the more famous ‘Wise Club’ had been at Aberdeen. Principal Leechman, Black, Moor, Arthur, and Dr. Thomas Hamilton were also members. Some of Reid’s contributions before 1788 seem to have been incorporated in the Essays. After that he still found vent for his thoughts in papers for the Society, and in letters to Dr. Gregory, chiefly about Power and Causation. Among the most important of those submitted to the Society in his last years, I find ‘Some Observations on the Modern System of Materialism,’ in which the impotence of matter is maintained; as also in another, entitled ‘Miscellaneous Reflections on Priestley’s account of Hartley’s Theory of the Human Mind.’ Then we have ‘Observations on the Utopia of Sir Thomas More.’ A short essay ‘On Power,’[24] in March 1792, was his last metaphysical performance: it sums up his conclusions regarding our conception of causation, as regulated by the Common Sense. ‘Observations on the Danger of Political Innovation,’ suggested by the Revolution in France, were read in the Society on November 1794.
This last Essay is characteristic. It presses a distinction between two political attitudes that are apt to be confounded—the one speculative, dealing with abstractions, treating the facts of the case and history as irrelevant; the other practical, taking account of the actual conditions, therefore disposed to modify its ideals by a due regard to what has been and now is. The first asks what that organisation of society is, which, abstractly considered, is most favourable to progress: the other cautiously considers how the inherited political organism may with least friction be adapted to the changed conditions of the social evolution. Reid assumes this last as his attitude, arguing that the British Constitution encourages continuous orderly evolution, not sudden revolution, and that this is illustrated in its history since 1688. At first, he had looked with sanguine hope to the French Revolution, but, like Edmund Burke, who shortly before had been Rector of Glasgow University, his hope gave place to fear. It is interesting that it was the Vindiciæ Gallicæ of Sir James Mackintosh that had inspired him with the hope; for, according to his daughter, Mrs. Carmichael, he was struck with admiration on reading the book, and used often to speak of it as one of the most ingenious essays in political philosophy he had ever met with.
Jeremy Bentham as well as Mackintosh was known to Reid by his writings, as appears in this letter to Dr. Gregory, in September 1788, which refers to Bentham’s Defence of Usury, published the year before:—
‘I am much pleased with the tract you sent me on Usury. I think the reasoning unanswerable, and have long been of the author’s opinion, though I suspect that the general principle—that bargains ought to be left to the judgment of the parties, may admit of some exceptions; when the buyers are the many, the poor, the simple, and the sellers few, rich, and cunning. The former may need the aid of the magistrate to prevent their being oppressed by the latter. It seems to be upon this principle that postage, freight, the hire of chairs and coaches, and the price of bread, are regulated in most great towns. But with regard to the loan of money in a commercial state, the exception can have no place—the borrowers and lenders are upon an equal footing, and each may be left to take care of his own interest.’