“There is always something about our feeling for beautiful things which can neither be described nor communicated, which is unshared and unshareable.”

The close of his Nobel lecture: "The Statistical Interpretations of Quantum Mechanics" (11 December 1954) http://nobelprize.org/nobel_prizes/physics/laureates/1954/born-lecture.html
Context: Can we call something with which the concepts of position and motion cannot be associated in the usual way, a thing, or a particle? And if not, what is the reality which our theory has been invented to describe?
The answer to this is no longer physics, but philosophy. … Here I will only say that I am emphatically in favour of the retention of the particle idea. Naturally, it is necessary to redefine what is meant. For this, well-developed concepts are available which appear in mathematics under the name of invariants in transformations. Every object that we perceive appears in innumerable aspects. The concept of the object is the invariant of all these aspects. From this point of view, the present universally used system of concepts in which particles and waves appear simultaneously, can be completely justified. The latest research on nuclei and elementary particles has led us, however, to limits beyond which this system of concepts itself does not appear to suffice. The lesson to be learned from what I have told of the origin of quantum mechanics is that probable refinements of mathematical methods will not suffice to produce a satisfactory theory, but that somewhere in our doctrine is hidden a concept, unjustified by experience, which we must eliminate to open up the road.

Pages 713–714.
"The Marxian Theory of Value: Das Kapital: A Criticism" (1884)
Context: It is true also that Marx elsewhere virtually defines value so as to make it essentially dependent upon human labour (p. 81 [43a]). But for all that his analysis is based on the bare fact of exchangeability. This fact alone establishes Verschiedenkeit and Ghichheit, heterogeneity and homogeneity. Any two things which normally exchange for each other, whether products of labour or not, whether they have, or have not, what we choose to call value, must have that "common something" in virtue of which things exchange and can be equated with each other; and all legitimate inferences as to wares which are drawn from the bare fact of exchange must be equally legitimate when applied to other exchangeable things. Now the "common something," which all exchangeable things contain, is neither more nor less than abstract utility, i. e. power of satisfying human desires. The exchanged articles differ from each other in the specific desires which they satisfy, they resemble each other in the degree of satisfaction which they confer. The Verschiedenheit is qualitative, the Gleichheit is quantitative.It cannot be urged that there is no common measure to which we can reduce the satisfaction derived from such different articles as Bibles and brandy, for instance (to take an illustration suggested by Marx), for as a matter of fact we are all of us making such reductions every day. If I am willing to give the same sum of money for a family Bible and for a dozen of brandy, it is because I have reduced the respective satisfactions their possession will afford me to a common measure, and have found them equivalent. In economic phrase, the two things have equal abstract utility for me. In popular (and highly significant) phrase, each of the two things is worth as much to me as the other.Marx is, therefore, wrong in saying that when we pass from that in which the exchangeable wares differ (value in use) to that in which they are identical (value in exchange), we must put their utility out of consideration, leaving only jellies of abstract labour. What we really have to do is to put out of consideration the concrete and specific qualitative utilities in which they differ, leaving only the abstract and general quantitative utility in which they are identical.This formula applies to all exchangeable commodities, whether producible in indefinite quantities, like family Bibles and brandy, or strictly limited in quantity, like the "Raphaels," one of which has just been purchased for the nation. The equation which always holds in the case of a normal exchange is an equation not of labour, but of abstract utility, significantly called worth. … A coat is made specifically useful by the tailor's work, but it is specifically useful (has a value in use) because it protects us. In the same way, it is made valuable by abstractly useful work, but it is valuable because it has abstract utility.

Source: The Faith of Leap (2011), p. 163

Source: Interest and Inflation Free Money (1995), Chapter Three, Who Would Profit From a New Monetary System?, p. 76

The New York Times (10 December 1916) From "Godlessness Mars Most Contemporary Poetry." http://query.nytimes.com/mem/archive-free/pdf?_r=1&res=9A0CE2D7153BE233A25753C1A9649D946796D6CF

Source: Letters to Milena

Book III, Ch. I, pp. 137-147.
Physics

Source: The Memorial and Instructions, pp. 151-152