“What's old collapses, times change,
And new life blossoms in the ruins.”

Hofnung un Shrek, 1906. Alle Verk, xiii. 9.

Human Nature and Social Theory (1969)
Context: One will be conducive to cooperation and solidarity another social structure to competition, suspiciousness, avarice; another to child-like receptiveness, another to destructive aggressiveness. All empirical forms or human needs and drives have to be understood as results of the social practice (in the last analysis based on the productive forces, class structure, etc., etc.) but they all have to fulfill the functions which are inherent in man’s nature in general, and that is to permit him to relate himself to others and share a common frame of reference, etc. The existential contradiction within man (to which I would now add also the contradiction between limitations which reality imposes on his life, and the virtually limitless imagination which his brain permits him to follow) is what I believe to be one of the motives of psychological and social dynamics. Man can never stand still. He must find solutions to this contradiction, and ever better solutions to the extent to which reality enables him.
The question then arises whether there is an optimal solution which can be inferred from man’s nature, and which constitutes a potential tendency in man. I believe that such optimal solutions can be inferred from the nature of man, and I have recently found it quite useful to think in terms of what in sociology and economy is now often called »system analysis«. One might start with the idea, in the first place, that human personality — just like society — is a system, that is to say, that each part depends on every other, and no part can be changed unless all or most other parts are also changed. A system is better than chaos. If a society system disintegrates or is destroyed by blows from the outside the society ends in chaos, and a completely new society is built upon its ruins, often using the elements of the destroyed system to build the new. That has happened many times in history. But, what also happens is that the society is not simply destroyed but that the system is changed, and a new system emerges which can be considered to be a transformation of the old one.

1960, The New Frontier
Context: But I think the American people expect more from us than cries of indignation and attack. The times are too grave, the challenge too urgent, and the stakes too high — to permit the customary passions of political debate. We are not here to curse the darkness, but to light the candle that can guide us through that darkness to a safe and sane future. As Winston Churchill said on taking office some twenty years ago: if we open a quarrel between the present and the past, we shall be in danger of losing the future. Today our concern must be with that future. For the world is changing. The old era is ending. The old ways will not do. [... ] It is a time, in short, for a new generation of leadership — new men to cope with new problems and new opportunities.

Selected Sonnets: A Bilingual Edition (2008), ed. William Baer, p. 70
Lyric poetry, Não pode tirar-me as esperanças, Mudam-se os tempos, mudam-se as vontades

Frankfurt Book Fair speech (2003)
Context: We are told we must choose — the old or the new. In fact, we must choose both. What is a life if not a series of negotiations between the old and the new? It seems to me that one should always be seeking to talk oneself out of these stark oppositions.

Source: The Worldly Philosophers (1953), Chapter VI, Karl Marx, p. 137