“All meaning is for an observer.”

Remarks after the Solvay Conference (1927)
Context: I consider those developments in physics during the last decades which have shown how problematical such concepts as "objective" and "subjective" are, a great liberation of thought. The whole thing started with the theory of relativity. In the past, the statement that two events are simultaneous was considered an objective assertion, one that could be communicated quite simply and that was open to verification by any observer. Today we know that 'simultaneity' contains a subjective element, inasmuch as two events that appear simultaneous to an observer at rest are not necessarily simultaneous to an observer in motion. However, the relativistic description is also objective inasmuch as every observer can deduce by calculation what the other observer will perceive or has perceived. For all that, we have come a long way from the classical ideal of objective descriptions.
In quantum mechanics the departure from this ideal has been even more radical. We can still use the objectifying language of classical physics to make statements about observable facts. For instance, we can say that a photographic plate has been blackened, or that cloud droplets have formed. But we can say nothing about the atoms themselves. And what predictions we base on such findings depend on the way we pose our experimental question, and here the observer has freedom of choice. Naturally, it still makes no difference whether the observer is a man, an animal, or a piece of apparatus, but it is no longer possible to make predictions without reference to the observer or the means of observation. To that extent, every physical process may be said to have objective and subjective features. The objective world of nineteenth-century science was, as we know today, an ideal, limiting case, but not the whole reality. Admittedly, even in our future encounters with reality we shall have to distinguish between the objective and the subjective side, to make a division between the two. But the location of the separation may depend on the way things are looked at; to a certain extent it can be chosen at will. Hence I can quite understand why we cannot speak about the content of religion in an objectifying language. The fact that different religions try to express this content in quite distinct spiritual forms is no real objection. Perhaps we ought to look upon these different forms as complementary descriptions which, though they exclude one another, are needed to convey the rich possibilities flowing from man's relationship with the central order.

The News Quiz, BBC Radio 4, July 1997 (rebroadcast on BBC 7, 23 July 1999)
Variant: It seems a shallow observation, but… the Tory Conference are not an attractive lot, are they? I mean, if all those people were born in the same village, you'd blame pollution, wouldn't you?

Pg. 67.
Against Method (1975)

Saanen, Switzerland (5 August 1973)
1970s
Context: Now, one sees all that by observing, by being aware, watching, one is aware of all this. Then out of that awareness you see there is no division between the observer and the observed. It is a trick of thought which demands security. Please don't madam, please. And by being aware it sees the observer is the observed, that violence is the observer, violence is not different from the observer. Now how is the observer to end himself and not be violent? Have you understood my question so far? I think so. Right? The observer is the observed, there is no division and therefore no conflict. And is the observer then, knowing all the intricacies of naming, linguistically caught in the image of violence, what happens to that violence? If the observer is violent, can the observer end, otherwise violence will go on? Can the observer end himself, because he is violent? Or what reality has the observer? Right sir? Is he merely put together by words, by experience, by knowledge? So is he put together by the past? So is he the past? Right? Which means the mind is living in the past. Right? obviously. You are living in the past. Right? No? As long as there is an observer there must be living in the past, obviously. And all our life is based on the past, memories, knowledge, images, according to which you react, which is your conditioning, is the past. And living has become the living of the past in the present, modified in the future. That's all, as long as the observer is living. Now does the mind see this as a truth, as a reality, that all my life is living in the past? I may paint most abstract pictures, write the most modern poems, invent the most extraordinary machinery, but I am still living in the past.

The News Quiz, BBC Radio 4, October 1998 (rebroadcast on BBC 7, 30 May 2006)

What is Art? (1897)

No. 15
On the Interpretation of Nature (1753)
Context: There are three principal means of acquiring knowledge available to us: observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination. Our observation of nature must be diligent, our reflection profound, and our experiments exact. We rarely see these three means combined; and for this reason, creative geniuses are not common.

See a person's “being”, observe his motive, notice his result. How can a person conceal his character? [by 朱冀平]
The Analects, Chapter I, Chapter II
Context: See a person's means (of getting things). Observe his motives. Examine that in which he rests. How can a person conceal his character?

De Abaitua interview (1998)