“I am capable of what every other human is capable of. This is one of the great lessons of war and life.”

Source: Sanitary Economy (1850), p. 28-29
Context: It has been among the visions of some dreaming philosophers that human life is capable of almost indefinite extension. The great Condorcet was one of these. He thought that by the removal of the two causes of evil—poverty and superfluity—by destroying prejudices and superstitions, and by various other operations, which he considered the purification of mankind, but which other people would call their pollution, the approach of death would by degrees be farther and farther indefinitely protracted. It is desirable that the practical views entertained by sanitary reformers should be kept widely distinct from any such theories, the character of which has been well drawn by Malthus when he says—"... Though I may not be able in the present instance to mark the limit at which further improvement will stop I can very easily mention a point at which it will not arrive."

Source: De Veritate (On Truth) q. 1, art. 2, ad 4

Source: Vanishing Acts

On the feedback received from other ATP World Tour players.
Source: João Sousa: "Partilho com o Nadal o gosto pelo Real Madrid" [Joao Sousa - 'I share with Nadal the fondness for Real Madrid' http://desporto.sapo.pt/mais_modalidades/tenis/artigo/2015/11/07/partilho-com-o-nadal-o-gosto-pelo-real-madrid,, SAPO, Portuguese, 9 November 2015]

Letter to Abigail Adams (29 October 1775), published Letters of John Adams, Addressed to His Wife, Vol. 1 (1841), ed. Charles Francis Adams, p. 72
1770s
Context: Human nature with all its infirmities and depravation is still capable of great things. It is capable of attaining to degrees of wisdom and goodness, which we have reason to believe, appear as respectable in the estimation of superior intelligences. Education makes a greater difference between man and man, than nature has made between man and brute. The virtues and powers to which men may be trained, by early education and constant discipline, are truly sublime and astonishing. Newton and Locke are examples of the deep sagacity which may be acquired by long habits of thinking and study.

Great Books: The Foundation of a Liberal Education (1954)

Source: Liber Null & Psychonaut (1987), p. 28
Context: Kia cannot be experienced directly because it is the basis of consciousness (or experience), and it has no fixed qualities which the mind can latch on to. Kia is the consciousness, it is the elusive "I" which confers self-awareness but does not seem to consist of anything itself. Kia can sometimes be felt as ecstasy or inspiration, but it is deeply buried in the dualistic mind. It is mostly trapped in the aimless wanderings of thought and in the identification with experience and in that cluster of opinions about ourselves called ego. Magic is concerned with giving the Kia more freedom and flexibility and with providing means by which it can manifest its occult power. Kia is capable of occult power because it is a fragment of the great life force of the universe.

Source: Eat, Pray, Love

Martí : Thoughts/Pensamientos (1994)
Context: To busy oneself with what is futile when one can do something useful, to attend to what is simple when one has the mettle to attempt what is difficult, is to strip talent of its dignity. It is a sin not to do what one is capable of doing.