Everything should be as simple as it is, but not simpler.

This saying is widely attributed to Albert Einstein as a maxim about scientific explanation and model-building: prefer the simplest account that still fits the facts, but do not oversimplify to the point of distortion. In Einstein’s milieu—early 20th‑century theoretical physics—there was constant pressure to reduce complex phenomena to elegant principles (as in relativity), while also respecting empirical constraints. However, the exact wording “Everything should be as simple as it is, but not simpler” is not securely traceable to a specific speech, letter, or publication by Einstein. It appears to be a later paraphrase of a sentiment he expressed in more formal terms about making theories as simple as possible without sacrificing adequacy.

The quote balances two intellectual virtues: parsimony and fidelity. It endorses simplicity as a guiding ideal—clear concepts, minimal assumptions, and economical explanations—because unnecessary complication obscures understanding. But it immediately adds a warning: simplicity is not the same as reductionism. If you simplify past the point where a description can capture relevant features of reality, you trade insight for a misleading neatness. In practice, it functions as advice for reasoning, writing, and theorizing: compress what can be compressed, yet keep the structure needed to remain true to the phenomenon. It is often invoked as a popular formulation of a “least complexity consistent with the data” principle.

1) "Everything should be made as simple as possible, but not simpler." 2) "Make everything as simple as possible, but not simpler." 3) "It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience."