Ebenezer Scrooge was visited by exactly three ghosts, not one, nor two, nor four. For all D’Artagnan’s heroism, Alexandre Dumas did not entitle his novel, The Four Musketeers. Trilogies and trinities are a lot more common, and popular, than tetralogies and quaternities (if that’s the word for them).

In rhetoric, three parallel words, clauses, or lines make up a tricolon, which is a particularly effective type of isocolon (or parallel construction).

• I came, I saw, I conquered. —Julius Caesar upon crossing the Rubicon
• Government of the people, by the people, for the people. —Abraham Lincoln in the Gettysburg Address
• Life, Liberty, and the Pursuit of Happiness. —The United States Declaration of Independence

Similar to tricolon is hendriatris, which involves the juxtaposition of three words to express a single idea or total concept, for example, Liberté, Egalité, Fraternité and ‘wine, women, and song’ (or, nowadays, ‘sex, drugs, and rock’n’roll’).

Winston’s Churchill’s first speech to the House of Commons as prime minister is remembered as Blood, Sweat, and Tears, even though he in fact said, ‘I have nothing to offer but blood, toil, tears, and sweat’. As prime minister, Tony Blair did not make his top priority ‘education, education’ but ‘education, education, education’. When asked a question, Joe Biden often responded by making just two points (‘Number 1… Number 2…’), leaving everyone to expect a non-forthcoming third.

Why is three so much more engaging, satisfying, and memorable than one or two or four? ‘Here are my three reasons.’ ‘I’ll give you three examples.’ ‘These are the three lessons I learnt.’

One is a fluke. Two is a coincidence. Four is one too many—to the extent that if you must have four, it might be better to present them as two linked pairs, and maybe add a third pair.

Three, however, is the smallest number required to create a pattern and rhythm—indeed, the rhythm of life, past, present, and future.

Triple goddesses or deities in groups of three are common in world myth: the Holy Trinity, the Tridevi, Hecate, Artemis, the Fates, the Furies, the Graces, the Græae, the Morrígan, the Norns… and, I believe, originally symbolized fate and the passage of time.

As a result, three is deeply embedded in our psyche.

Neel Burton is author of How to Think Like Plato and Speak Like Cicero.