All three Greek words denote causal powers that are beyond the reach of human control, and hence were often personified as goddesses.
The word "moira" means a share, part, or portion, and by derivation, the fate allotted to a person. In mythological contexts, it was personified either as a single goddess or, as in Hesiod's Theogony and in the myth of Plato's Republic X, as a group of three goddesses (Clotho, Lachesis, Atropos). Moira or the Moirai determine the fate of individuals by "spinning" the thread of one's life. The word "moira" sometimes euphemistically refers to death, as the fate of all humans. In other contexts it refers to one's rank or distinction or to the positive abilities allotted by the gods, such as poetic inspiration. In Stoic determinism, it is used in relation to universal fate (heimarmenē ).
The noun "tychē" (fortune) is related to the verb "tynchano" (happen, befall). Tychē was taken to be the cause of chance events—events that one could not or did not calculate and that do not fit into a regular pattern. While moira determines one's course of life as a whole, tychē tends to be responsible for singular events of varying importance. The connotations of the word were originally more positive, but by Hellenistic times it regularly had the pejorative meaning of blind, impersonal, arbitrary chance. In philosophical contexts it is most often contrasted with rational choice and goal-driven action. Plato, in the Laws X, grouped tychē together with the mechanistic force of nature and opposed it to the rational, purposeful activity of a cosmic god. Aristotle, in the Physics II.5–7, classified tychē under spontaneity (automaton ) and defined it as an accidental and indeterminable cause in the sphere of purposeful actions involving rational choice. In other words, tychē for Aristotle is the cause of events that might have been the outcome of rational human choice but in fact are not.
The word "anankē" originally referred to an external constraining force, and from this meaning it obtained the more abstract meaning of logical and physical necessity during the pre-Socratic period. It is often represented as the ultimate power with which even the gods must comply. In Parmenides' Aletheia, the personified Anankē guarantees that Being is unchangeable and immobile, and "holds [Being] in the bonds of a limit" (Diels and Kranz 1954, B8.30), while in the Doxa she keeps the starry heaven enchained (B11.6). In Empedocles' writings, Anankē's oracle sets the punishment of those who commit the ultimate sin of bloodshed (B115.1). In the myth of Plato's Republic X, Anankē is the mother of the three Moirai. Her function is primarily cosmological in that she holds a spindle whose movement stands for the celestial motions. In Plato's Timaeus, anankē is the regular but nonteleological causal force inherent in the physical realm. Insofar as the physical properties of the elements can be put into the service of the purposeful activity of reason, anankē becomes the auxiliary cause (sunaition ) in teleological causation. Aristotle's distinction between simple and hypothetical necessity in the Physics II.9 shows clear traces of the conception of anankē in the Timaeus.
Cornford, Francis Macdonald. Plato's Cosmology. London: Routledge and Kegan Paul, 1937.
Diels, Hermann, and Walther Kranz. Die Fragmente der Vorsokratiker. 7th, rev. ed. Berlin: Weidmann, 1954.
Dietrich, Bernard Clive. Death, Fate, and the Gods: The Development of a Religious Idea in Greek Popular Belief and in Homer. London: Athlone Press, 1965.
Schreckenberg, Heinz. Ananke: Untersuchungen zur Geschichte des Wortgebrauchs. Munich, Germany: C. H. Beck'sche Verlagsbuchhandlung, 1964.
Gábor Betegh (2005)