“Reality contains not only evidence, but also the means (such as our minds, and our artefacts) of understanding it. There are mathematical symbols in physical reality. The fact that it is we who put them there does not make them any less physical.”
Source: The Fabric of Reality (1997), Ch.3
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David Deutsch 20
British physicist 1953Related quotes

“Reality must be expressed by a physical symbol.”
Bahai lecture, New York, October 30, 1951; as quoted in Abstract Expressionist Painting in America, W.C, Seitz, Cambridge Massachusetts, 1983, p. 10
1950's

George Herbert Mead (1926). "The Nature of Aesthetic Experience." International Journal of Ethics, Vol. 36, No. 4 (Jul., 1926), pp. 382-393; p. 382

Source: Light on Life: The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom, p. 9

Science and the Unseen World (1929)
Context: It remains a real world if there is a background to the symbols—an unknown quantity which the mathematical symbol x stands for. We think we are not wholly cut off from this background. It is to this background that our own personality and consciousness belong, and those spiritual aspects of our nature not to be described by any symbolism... to which mathematical physics has hitherto restricted itself.<!--III, p.37-38

“Ego is a social institution with no physical reality. The ego is simply your symbol of yourself.”
Buddhism : The Religion of No-Religion
Context: Ego is a social institution with no physical reality. The ego is simply your symbol of yourself. Just as the word "water" is a noise that symbolizes a certain liquid without being it, so too the idea of ego symbolizes the role you play, who you are, but it is not the same as your living organism.