Those _Essays_ of Reid which treat of the constituents of the common sense that are implied in the Intellect power of man, appeared in the early summer of 1785. In September he informed Dr. Gregory of the opinion of Dr. Price, the most eminent contemporary English metaphysician:—‘I had a letter from Dr. Price lately, thanking me for a copy of the _Essays_ I ordered to be presented to him; which he has read, and calls a work of the first value; commends me particularly for treating Dr. Priestley so gently, who, he says, had been unhappily led to use me ill.’ He then refers to his own health, which seems to have suffered from the mental strain, now relieved by the issue of his book:—‘As you are so kind as to ask me about my distemper, I think it is almost quite gone, so as to give me no uneasiness. I abstain from fruit and malt liquor, and take a little port wine, mostly noon and night, not above two bottles a week when alone. The more I walk or ride, or even talk or read audibly, I am the better.’ Dr. Beattie writes thus to the Bishop of Chester in October:— ‘Has your lordship read Dr. Reid’s _Essays on the Intellectual Powers of Man_? Those readers who have been conversant in the modern philosophy of mind, as it appears in the writings of Descartes, Malebranche, Locke, Berkeley, and Hume, will be much entertained with this work, which does great honour to the sagacity and patience of the author. It contains the principles of his _Inquiry_, laid down on a larger scale, and applied to a greater variety of subjects. Dr. Reid treats his opponents and their tenets with a respect and a solemnity that sometimes tempt me to smile. His style is clear and simple; and his aversion to the word _idea_ is so great, that I think he never once uses it in delivering his own opinions. It was not without reason that Stillingfleet took the alarm at Mr. Locke’s indiscreet use of that word. It was indeed an _ignis fatuus_ that decoyed him in spite of his excellent understanding into a thousand pits and quagmires. Berkeley it bewildered still more. And it reduced David Hume to the condition of a certain old gentleman of whom we read, that— Fluttering his pinions vain, Plumb down he dropped, ten thousand fathoms deep.’ Whether our power of conceiving is so far a test of possibility, as that what is distinctly conceived must be concluded to be possible, and what cannot be conceived impossible, was a question which interested Reid. It is discussed in the _Essays on the Intellectual Powers_, and also in the draft of a letter to Dr. Price, preserved among the manuscripts at Birkwood; in which it is argued that our power of conception cannot be a criterion of what is possible. The argument turns much on the meanings of ‘conception,’ ‘possibility,’ and ‘impossibility.’ He thus addresses Dr. Price:—