Critique of Pure Reason

For human reason, without any instigations imputable to the mere vanity of great knowledge, unceasingly progresses, urged on by its own feeling of need, towards such questions as cannot be answered by any empirical application of reason, or principles derived therefrom; and so there has ever really existed in every man some system of metaphysics.

The real morality of actions—their merit or demerit, and even that of our own conduct, is completely unknown to us. Our estimates can relate only to their empirical character. How much is the result of the action of free will, how much is to be ascribed to nature and to blameless error, or to a happy constitution of temperament (merito fortunae), no one can discover, nor, for this reason, determine with perfect justice.

The understanding cannot intuit anything, the senses cannot think anything. Only from their union can knowledge arise.

Any attempt at using logic as a tool (organon) in order to extend and expand our knowledge, at least supposedly, can end in nothing but idle talk, where one can assert or, if one prefers, deny, anything one likes, with a certain semblance of plausibility.

To coin new words is to arrogate to oneself legislative power in matters of language, which is rarely successful [...]

The world of sense, if it is limited, lies necessarily within the infinite void. If we ignore this, and with it, space in general, as an a priori condition of the possibility of phenomena, the whole world of sense vanishes, which alone forms the object of our enquiry.

At the beginning of modern science, a light dawned on all those who study nature. They comprehended that reason has insight only into what it itself produces according to its own design; that it must take the lead with principles for its judgments according to constant laws and compel nature to answer its questions, rather than letting nature guide its movements by keeping reason, as it were, in leading-strings; for otherwise accidental observations, made according to no previously designed plan, can never connect up into a necessary law, which is yet what reason seeks and requires. Reason, in order to be taught by nature, must approach nature with its principles in one hand, according to which alone the agreement among appearances can count as laws, and, in the other hand, the experiments thought in accordance with these principles - yet in order to be instructed by nature not like a pupil, who has recited to him whatever the teacher wants to say, but like an appointed judge who compels witnesses to answer the questions he puts to them. Thus even physics owes the advantageous revolution in its way of thinking to the inspiration that what reason would not be able to know of itself and has to learn from nature, it has to seek in the latter (though not merely ascribe to it) in accordance with what reason itself puts into nature. This is how natural science was first brought to the secure course of a science after groping about for so many centuries.

Starry heavens above me and the moral law within me.

Freedom (independence) from the laws of nature is no doubt a liberation from restraint, but also from the guidance of all rules.

Reason only perceives that which it produces after its own design.

I cannot, therefore, perceive external things, but can only infer their existence from my own inner perception, by taking the perception as the effect of which something external must be the proximate cause.

For with regard to nature, it is indeed experience which supplies us with the rule and is the source of truth; with regard to moral laws, however, experience is, alas!, but the mother of illusion; and it is altogether reprehensible either to derive or to try to limit the laws of what we ought to do from what is done.