“A serious student of philosophy will be in no haste to accept or reject this doctrine; but he will see in it one of the chief attitudes which speculative thought may take, feeling that it is not for an individual, nor for an age, to pronounce upon a fundamental question of philosophy. That is a task for a whole era to work out.”

The Myth of Sisyphus and other essays by Albert Camus, An Absurd Reasoning : Absurdity and Suicide p. 3 (1942, 1955)
Absurdity and Suicide
The Myth of Sisyphus (1942), An Absurd Reasoning
Context: There is but one truly serious philosophical problem and that is suicide. Judging whether life is or is not worth living amounts to answering the fundamental question of philosophy. All the rest – whether or not the world has three dimensions, whether the mind has nine or twelve categories – comes afterwards. These are games; one must first answer. And if it is true, as Nietzsche claims, that a philosopher, to deserve our respect, must preach by example, you can appreciate the importance of that reply, for it will precede the definitive act. These are facts the heart can feel; yet they call for careful study before they become clear to the intellect. If I ask myself how to judge that this question is more urgent than that, I reply that one judges by the actions it entails. I have never seen anyone die for the ontological argument.

Letter to Can Grande (Epistle XIII, 40), as translated by Charles Latham in A Translation of Dante's Eleven Letters (1891), Letter XI, §16, p. 199.
Epistolae (Letters)

Reminiscences (1881), referring to his father, James Carlyle.
Sometimes quoted as "Man was created to work, not to speculate, or feel, or dream; Every idle moment is treason". The second of those two clauses in fact comes from Thomas Arnold The Christian Life (1841), Lecture VI.
1880s

Variant translation: Philosophy is not a theory but an activity. A philosophical work consists essentially of elucidations. The result of philosophy is not a number of "philosophical propositions." but to make propositions clear.
Original German: Der Zweck der Philosophie ist die logische Klärung der Gedanken. Die Philosophie ist keine Lehre, sondern eine Tätigkeit. Ein philosophisches Werk besteht wesentlich aus Erläuterungen. Das Resultat der Philosophie sind nicht „philosophische Sätze“, sondern das Klarwerden von Sätzen. Die Philosophie soll die Gedanken, die sonst, gleichsam, trübe und verschwommen sind, klar machen und scharf abgrenzen.
1920s, Tractatus Logico-Philosophicus (1922)
Context: Philosophy aims at the logical clarification of thoughts. Philosophy is not a body of doctrine but an activity. A philosophical work consists essentially of elucidations. Philosophy does not result in 'philosophical propositions', but rather in the clarification of propositions. Without philosophy thoughts are, as it were, cloudy and indistinct: its task is to make them clear and to give them sharp boundaries. (4.112)

Classic, Romantic, Modern (1961), ch. I: "Romanticism — Dead or Alive?"

An Old Man's Thoughts on Many Things, Of Education I
Context: By drawing an object the children will also learn a fundamental doctrine of philosophy; but I don't recommend letting them know what the doctrine is. They will discover it some time. We do not draw objects as they are: we draw them as they seem to be. To the eye things are what they seem to be, but they are in reality, if you know what that means, something else.

Source: Philosophy and the Return to Self-Knowledge (1997), p. 191

"Philosophy" (1929) as quoted by Nils-Eric Sahlin, The Philosophy of F. P. Ramsey (1990)

Source: A New Model of the Universe (1932), p. 33
Context: Philosophy is based on speculation, on logic, on thought, on the synthesis of what we know and on the analysis of what we do not know. Philosophy must include within its confines the whole content of science, religion and art. But where can such a philosophy be found? All that we know in our times by the name of philosophy is not philosophy, but merely "critical literature" or the expression of personal opinions, mainly with the aim of overthrowing and destroying other personal opinions. Or, which is still worse, philosophy is nothing but self-satisfied dialectic surrounding itself with an impenetrable barrier of terminology unintelligible to the uninitiated and solving for itself all the problems of the universe without any possibility of proving these explanations or making them intelligible to ordinary mortals.