“London times – the untiring energy, the business-like accuracy, the keen perception and reliable judgment, and above all the inflexible integrity which marked his private life, he carried without abatement of one jot into his public career.”

Draft for a Statement of Human Obligation (1943)
Context: Anyone whose attention and love are really directed towards the reality outside the world recognizes at the same time that he is bound, both in public and private life, by the single and permanent obligation to remedy, according to his responsibilities and to the extent of his power, all the privations of soul and body which are liable to destroy or damage the earthly life of any human being whatsoever.
This obligation cannot legitimately be held to be limited by the insufficiency of power or the nature of the responsibilities until everything possible has been done to explain the necessity of the limitation to those who will suffer by it; the explanation must be completely truthful and must be such as to make it possible for them to acknowledge the necessity.
No combination of circumstances ever cancels this obligation. If there are circumstances which seem to cancel it as regards a certain man or category of men, they impose it in fact all the more imperatively.
The thought of this obligation is present to all men, but in very different forms and in very varying degrees of clarity. Some men are more and some are less inclined to accept — or to refuse — it as their rule of conduct.

“Individuality and Modernity,” Essays on Individuality (Philadelphia: 1958), p. 72.

Source: Man for Himself (1947), p.189

Thoughts on the Cause of the Present Discontents (1770)

Part 2, Book 1, Ch. 2
Ninety-Three (1874)
Context: Cimourdain was one of those men who have a voice within them, and who listen to it. Such men seem absent-minded; they are not; they are all attention.
Cimourdain knew everything and nothing. He knew everything about science, and nothing at all about life. Hence his inflexibility. His eyes were bandaged like Homer's Themis. He had the blind certainty of the arrow, which sees only the mark and flies to it. In a revolution, nothing is more terrible than a straight line. Cimourdain went straight ahead, as sure as fate.
Cimourdain believed that, in social geneses, the extreme point is the solid earth; an error peculiar to minds which replace reason with logic.

Though at times attributed to Leary on the internet, no published source of this has been located. It is a misquote of a William S. Burroughs reading entitled M.O.B. from the Giorno Poetry Systems boxed set. M.O.B. was an extension of Burroughs' expression in The Place of Dead Roads (1983), p. 155:
You are a Shit Spotter. It's satisfying work. … We have observed that most of the trouble in the world has been caused by ten to twenty percent of folks who can't mind their own business, because they have no business of their own to mind, any more than a smallpox virus … The mark of a basic shit is that he has to be right.
Misattributed

Introductory. Pearson refers the reader to William Wordsworth's preface to the Lyrical Ballads (1815) "General View of Poetry".
The Grammar of Science (1900)