"On the Method of Theoretical Physics" The Herbert Spencer Lecture, delivered at Oxford (10 June 1933); also published in Philosophy of Science, Vol. 1, No. 2 (April 1934), pp. 163-169., p. 165. [thanks to Dr. Techie @ www.wordorigins.org and JSTOR]
There is a quote attributed to Einstein that may have arisen as a paraphrase of the above quote, commonly given as “Everything should be made as simple as possible, but no simpler,” "Everything should be made as simple as possible, but not simpler", or “Make things as simple as possible, but not simpler.” See this article from the Quote Investigator http://quoteinvestigator.com/2011/05/13/einstein-simple/ for a discussion of where these later variants may have arisen.
The original quote is very similar to Occam's razor, which advocates that among all hypotheses compatible with all available observations, the simplest hypothesis is the most plausible one.
The aphorism "everything should be made as simple as possible, but no simpler" is normally taken to be a warning against too much simplicity and emphasizes that one cannot simplify things to a point where the hypothesis is no more compatible with all observations. The aphorism does not contradict or extend Occam's razor, but rather stresses that both elements of the razor, simplicity and compatibility with the observations, are essential.
The earliest known appearance of Einstein's razor is an essay by Roger Sessions in the New York Times (8 January 1950) http://select.nytimes.com/gst/abstract.html?res=F30615FE3559137A93CAA9178AD85F448585F9, where Sessions appears to be paraphrasing Einstein: “I also remember a remark of Albert Einstein, which certainly applies to music. He said, in effect, that everything should be as simple as it can be, but not simpler.”
Another early appearance, from Time magazine (14 December 1962) http://www.time.com/time/magazine/article/0,9171,872923,00.html: “We try to keep in mind a saying attributed to Einstein—that everything must be made as simple as possible, but not one bit simpler.”
1930s
“No goal, regardless of how small can be achieved without adequate training.”
Ch. 1 : Experience as evidence http://www.marxists.org/reference/subject/philosophy/works/en/laing.htm
The Politics of Experience (1967)
Context: Even facts become fictions without adequate ways of seeing "the facts". We do not need theories so much as the experience that is the source of the theory. We are not satisfied with faith, in the sense of an implausible hypothesis irrationally held: we demand to experience the "evidence".
We can see other people's behaviour, but not their experience. This has led some people to insist that psychology has nothing to do with the other person's experience, but only with his behaviour.
The other person's behaviour is an experience of mine. My behaviour is an experience of the other. The task of social phenomenology is to relate my experience of the other's behaviour to the other's experience of my behaviour. Its study is the relation between experience and experience: its true field is inter-experience.
Source: Complexity and Postmodernism (1998), p. ix
As quoted in Physics by Aristotle, as translated by John Burnet http://www.classicpersuasion.org/pw/burnet/egp.htm?pleaseget=14
Context: There cannot be a single, simple body which is infinite, either, as some hold, one distinct from the elements, which they then derive from it, nor without this qualification. For there are some who make this (i. e. a body distinct from the elements) the infinite, and not air or water, in order that the other things may not be destroyed by their infinity. They are in opposition one to another — air is cold, water moist, and fire hot—and therefore, if any one of them were infinite, the rest would have ceased to be by this time. Accordingly they say that what is infinite is something other than the elements, and from it the elements arise.
Source: 1980s, Against The Grain (1986), Ch. 10, The Critic as Clown
“Experience without theory is blind, but theory without experience is mere intellectual play.”
This is declared to be "an old Kantian maxim" in General Systems Vol. 7-8 (1962), p. 11, by the Society for the Advancement of General Systems Theory, but may simply be a paraphrase or summation of Kantian ideas.
Kant's treatment of the transcendental logic in the First Critique contains a portion, of which this quote may be an ambiguously worded paraphrase. Kant, claiming that both reason and the senses are essential to the formation of our understanding of the world, writes: "Without sensibility no object would be given to us, and without understanding none would be thought. Thoughts without content are empty, intuitions without concepts are blind (A51/B75)".
Disputed
“Few of us can easily surrender our belief that society must somehow make sense.”
Why I Wrote 'The Crucible in The New Yorker (21 October 1996) https://archive.is/20130630000741/www.newyorker.com/archive/content/?020422fr_archive02
Context: Few of us can easily surrender our belief that society must somehow make sense. The thought that the state has lost its mind and is punishing so many innocent people is intolerable. And so the evidence has to be internally denied.
