Adam Smith, from Lectures on Rhetoric and Belles Lettres:

There is perhaps no English writer who has more of this Gaiety than Mr Addison, neither has he so much as Lucian. This is the chief character of all his prose works: he frequently in the manner of Lucian begins his discourses with a story which he places before the subject itself, as in his address to the Tory Ladies in the Freeholder; but he never carries these so far as Lucian does, nor so minutely. This perhaps may be owing to a sort of modesty which he is said to have been possessed in a very great degree, in the common affairs of life and which breaths indeed thro all his works and which the other author does not appair to have had in any considerable share, from severall stories he tells of himself, as that of his biting the thumb of the Imposter Alexander. The Ludicrous incident of biting Alexanders thumb is related in his Life of that imposter, than which few things are more entertaining. His modesty hinders him from those bold and extravagant strokes of humour which Lucian uses (he would not for instance put a Ludicrous speech into the mouths of a dead man or a god) or from throwing out such biting sarcasms in his own person as Swift often does. The flowryness of Mr Addison naturally lead him to make frequent use of figures in his discourses, the chief of these are metaphors, similies and Allegories. But in the use of these he always displays the modesty of his character. It may seem strange how the use of Allegories especially should seem consistent with that modesty we have attributed to him as they are the boldest and strongest kind of figures, but the manner in which he introduces them is always such as makes it appear that there was nothing forced or uneasy in the reforming them. [Spec 55, 63, 183, 315, 464] He often introduces them in the form of a dream,[FT: Tat.81, 97, 100, 117, 119, 120, 123, 146, 154, 161; Spec 110, 159, 275, 487, 505, 558-9] and at the same time shews us the train of thought that led him into such conceptions, and by this means makes us imagine that the circumstances he was in naturally Suggested them without his being at any pains about it. As that where he compares the different characters of men to different musicall instruments. [Tat 153]

In the same manner his similes are always represented as naturally presenting themselves. This modesty we have ascribed to him causes him likewise deliver his sentiments in the least assuming manner; and this would incline him rather to narrate what he had seen and heard than to deliver his opinions in his own person; and at the same time he will not seem to be at great pains to give nice and curious circumstances; it is more consistent with the naturall modesty of his temper to give us only a few of the most striking and interesting. He neither presumes as Shaftesbury and Bollingbroke, nor dictates as Swift. Shaftesbury and Bolinbroke display their superior dignity etc. Swift his superiority of Sense. For the same reason he neither writes with the precision and nice propriety of the latter, nor have his sentences that Uniform cadence in their severall members as the two former writers always affected. His Sentences are neither long nor short but of a length suited to the character he has of a modest man; who naturally delivers himself in Sentences of a moderate length and with a uniform tone. Accordingly we find those of Mr Addeson are of this sort. They generally consist of 3, 4 or 5 phrases and are so uniform in their manner that we read them with a sort of monotony. The modest man will not use long sentences as they are either proper for declamation, which he never uses, or bespeak a confusion of Ideas that is not to be attributed to Mr Addison. He would not either deliver himself in short sentences, as that would appear either like Snip-snap or the language of presumption and a dictating temper. As he does not pretend that every thing he says is of the utmost importance, and an infallible rule, so he is much more lax in his writings than Dr Swift: every word of his writings is of importance; when on the other hand Mr Addison frequently turns up the same thought in the different phrases of a sentence only placing it in a different light, and is rather inaccurate in the use of words and reptition of Synonymes, which the concluding of the Essay on the Pleasures of the imagination [Spec 411-421] will be an example of if examined with that view.

He frequently makes quotations from the Poets, which gives his writings an air of gaiety and good humour. This Gaiety joined to the modesty that appears in his works has gained him the character of a most polite and elegant writer. His descriptions are not near so animated as those of Lucian, and this may proceed both from his naturall modesty and from his imagination not being altogether so lively. This will appear to be the case in any of his descriptions if compared with that of Jupiter carrying of Europa in Lucian which is remarkably animated, and gives as compleat a notion of the severall transactions as words can convey.

-- Lectures on Rhetoric and Belles Lettres, ed, J. C. Bryce (Indianapolis: Liberty Fund, 1985), pp. 52-54. (N. B. Constructed from manuscript notes, this edition includes editorial marks to indicate deleted phrases and ambiguities in the manuscript. Such marks are left out here.)

James Boswell, from London Journal:

1 December 1762

After my wild expedition to London in the year 1760, after I got rid of the load of serious reflection which then burthened me, by being always in Lord Eglinton’s company, very fond of him, and much caressed by him, I became dissipated and thoughtless. When my father forced me down to Scotland, I was at first very low-spirited, although to appearance very high. I afterwards from my natural vivacity endeavoured to make myself easy; and like a man who takes to drinking to banish care, I threw myself loose as a heedless, dissipated, rattling fellow who might say or do every ridiculous thing. This made me sought after by everybody for the present hour, but I found myself a very inferior being; and I found many people presuming to treat me as such, which notwithstanding of my appearance of undiscerning gaiety, gave me much pain. I was, in short, a character very different from shat GOD intended me and I myself chose. I remember my friend Johnston told me one day after my return from London that I had turned out different from what he imagined, as he thought I would resemble Mr. Addison. I laughed and threw out some loud sally of humour, but the observation struck deep. Indeed, I must do myself the justice to say that I always resolved to be such a man whenever my affairs were made easy and I got upon my own footing. For as I despaired of that, I endeavoured to lower my views and just to be a good-humoured comical being, well liked either as a waiter, a common soldier, a clerk in Jamaica, or some other odd out-of-the-way sphere. Now, when my father at last put me into an independent situation, I let my mind regain its native dignity. I felt strong dispositions to be a Mr. Addison. Indeed, I had accustomed myself so much to laugh at everything that it required time to render my imagination solid and give me just notions of real life and of religion. But I hoped by degrees to attain to some degree of propriety. Mr. Addison’s character in sentiment, mixed with a little of the gaiety of Sir Richard Steele and the manners of Mr. Digges, were the ideas which I aimed to realize.

5 December 1762

Swift, Journal to Stella