What Is an Omen? Reading the Future in Things That Already Happened

Divination systems divide broadly into those reading signs that arrive unbidden and those producing signs deliberately. Unsolicited omens include the flight and calls of birds, the behaviour of animals, unusual weather, births of malformed animals, eclipses and dreams, all of which occur anyway and are interpreted when they do. Solicited ones involve generating a sign on request, by inspecting the liver of a sacrificed animal, casting lots, heating a bone or shell until it cracks, or consulting a text at random. The two differ in an important respect, since a system that produces an answer on demand can be used for specific decisions at chosen moments, which makes it administratively useful in a way that waiting for a bird is not. That is why solicited methods dominate in state contexts, and why the technical literature that survives, particularly from Mesopotamia, concerns liver inspection and celestial observation rather than casual signs.

The infrastructure surrounding divination in several ancient states was substantial:

• •Mesopotamian scholars maintained enormous compendia of omens and their interpretations, running to thousands of entries organised systematically, which functioned as reference works
• •Liver models in clay, marked with regions and meanings, were used for training, and examples survive
• •Chinese oracle bone divination from the Shang period produced inscriptions recording the question, the result and sometimes the outcome, and those inscriptions are the earliest substantial body of Chinese writing
• •Roman practice included official augurs whose approval was required before public business, and an unfavourable reading could halt an assembly or a campaign
• •Greek oracle sites received consultations from states as well as individuals and their pronouncements influenced colonisation, warfare and law
• •Astrological practice in several traditions was a mathematical discipline requiring genuine astronomical competence, and the observational records kept for it are scientifically valuable

Dismissing divination as mere superstition misses what it was doing. It provided a decision procedure in situations where information was genuinely unavailable and a choice had to be made, which is a real problem and one that modern organisations solve with less transparency. It distributed responsibility away from the individual deciding, which made unpopular decisions possible. It created a pause and a formal moment of deliberation before action. It could be checked in a limited way, since some systems recorded outcomes, and the Mesopotamian compendia are organised as accumulated experience rather than as arbitrary assertion. It also functioned as a randomiser in circumstances where unpredictability is useful, which is a genuine strategic advantage and has been argued as an explanation for practices including divination-directed hunting, where randomising where to hunt prevents prey learning to avoid a pattern.

The practice did not end and its modern forms are recognisable once the category is clear. Weather lore attaches predictions to observable signs, some of which have a physical basis, since a red sky does carry information about the atmosphere to the west, and most of which do not. Superstitions around luck read events as indicators, with broken mirrors, magpies, black cats and spilled salt functioning exactly as omens do, and studies find that a substantial minority of people in wealthy secular countries act on at least one. Sporting rituals are omen-adjacent, since a player who repeats a sequence that preceded a win is treating the sequence as connected to the outcome. Financial markets generate their own, with commentators identifying indicators whose predictive record is no better than chance and which persist because a few striking successes are remembered. Medical and political commentary produce the same, with early signs treated as diagnostic of an outcome that is genuinely uncertain, which is the original practice performed with different vocabulary.

Several well-documented cognitive effects make a divination system feel accurate regardless of whether it is. Confirmation bias means that fulfilled predictions are remembered and failures are forgotten or reinterpreted. Ambiguity is a feature rather than a defect, since a pronouncement capable of more than one reading is fulfilled whatever happens, which is exactly what the famous Delphic responses did. Self-fulfilling prophecy operates when a prediction changes behaviour in ways that bring it about, which is entirely real. Post hoc reinterpretation adjusts the meaning after the event. And the base rate of predicted events is frequently high, since predicting conflict, illness or a bad harvest is predicting something likely. None of that requires anyone to be deceiving anybody, and practitioners were generally sincere, which is why the practices persisted for millennia among people who were not credulous about other matters.

Signs arriving unbidden and signs produced on demand differ in usefulness, since a method that answers when asked can be attached to a specific decision, which is why state practice centred on liver inspection and the heavens. Mesopotamian compendia ran to thousands of systematically organised entries. The practice supplied a decision procedure where information was absent and distributed responsibility away from the person choosing.