Invention is not the product of logical thought, even though the final product is tied to a logical structure.
The thoughts that come often unsought, and, as it were, drop into the mind, are commonly the most valuable of any we have, and therefore should be secured, because they seldom return again.
You could attach prices to thoughts. Some cost a lot, some a little. And how does one pay for thoughts? The answer, I think, is: with courage.[Man könnte Gedanken Preise anheften. Manche kosten viel, manche wenig. Und womit zahlt man für Gedanken? Ich glaube: mit Mut.]
Without Freedom of Thought, there can be no such Thing as Wisdom; and no such Thing as publick Liberty, without Freedom of Speech.
When a man after long years of searching chances on a thought which discloses something of the beauty of this mysterious universe, he should not therefore be personally celebrated. He is already sufficiently paid by his experience of seeking and finding. In science, moreover, the work of the individual is so bound up with that of his scientific predecessors and contemporaries that it appears almost as an impersonal product of his generation.