Spontaneous order
Spontaneous order is order that arises from the interaction of many individuals pursuing their own purposes, without any of them intending the resulting pattern and without direction from above. Adam Ferguson's formulation, which Friedrich Hayek took as the motto of the idea, is that such institutions are the result of human action but not of human design.
The concept is central to the Austrian School because it identifies a third possibility between things that are natural and things that are deliberately made, and most of the institutions economics studies fall into it.
Menger on the origin of money
Carl Menger supplied the model case. Money is not plausibly explained as a natural phenomenon, and the older theory that it was established by a ruler or a social compact merely relocates the puzzle. Menger showed instead how money emerges without anyone intending it: in barter a trader improves his position by accepting a good he does not want himself if it is more saleable than what he holds, since it eases his next exchange. As traders converge on the most saleable goods for this reason, those goods become general media of exchange. No one set out to invent money; each was solving his own problem.[1]
The same pattern was applied by Menger and later writers to language, law, custom and the division of labor.
Hayek: knowledge and the limits of design
Friedrich Hayek developed the idea into an argument about knowledge. The information needed to coordinate an economy is particular, local, often tacit, and continually changing. It exists only in dispersed form across millions of people and is not available to any mind or committee in aggregate form. Prices work as a mechanism for conveying just enough of it: a rise tells everyone using a good to economise on it without telling them why, and the adjustment proceeds without anyone possessing the whole picture.[2]
Central direction fails on this account not because planners are stupid or wicked but because the knowledge they would need does not exist in a form anyone could be given. This is a different objection from Mises's calculation argument, though the two are complementary and are often run together.
Hayek marked the contrast with a pair of Greek terms: cosmos, a grown order, against taxis, a made order such as a firm or an army. A grown order can be far more complex than anything designed, because it is not limited by what one mind can hold; but for the same reason it cannot be given specific ends, and the demand that the market produce a particular distribution asks of a cosmos something only a taxis could deliver.
Misreadings
Spontaneous order is regularly mistaken for two claims it does not make. It does not say that undesigned outcomes are always good: Hayek held that grown institutions are subject to selection over time, not that whatever emerges is thereby justified, and traditions can persist that no longer serve. Nor does it say that deliberate organisation is illegitimate. Firms are designed orders, and the argument concerns the level at which design is possible, not whether anyone may plan anything.