Greek Alphabet

Why science runs on Greek letters

There are only 26 Latin letters and vastly more quantities to name. Mathematics and physics borrowed a second alphabet, and over time strong conventions attached to particular letters.

Those conventions matter. Seeing λ in a physics paper, a reader assumes wavelength until told otherwise. Using it for something else is legal and unkind.

The ones that carry the most weight

• Δ delta — change in something. Δt is an interval of time. Lowercase δ means an infinitesimally small change.
• Σ sigma — capital means "sum of". Lowercase σ is standard deviation, which is why statisticians talk about three-sigma events.
• π pi — 3.14159. Capital Π means "product of", the multiplicative twin of Σ.
• μ mu — the micro- prefix, so μm is a micrometre. Also the population mean.
• Ω omega — ohms. Lowercase ω is angular velocity.
• λ lambda — wavelength, and eigenvalues in linear algebra.

Two letters nobody uses

Omicron and iota are essentially absent from notation, because lowercase omicron is indistinguishable from the letter o and iota is too close to i. A symbol that cannot be told apart on a blackboard is useless.

This is also why the World Health Organization skipped Nu and Xi when naming coronavirus variants and jumped to Omicron — Nu sounds like "new" and Xi is a common surname.

Saying them out loud

The pronunciations above are the conventional English-speaking scientific ones, which differ from both modern and ancient Greek. χ is said "kye" in English maths and something closer to a throaty "kh" in Greek; β is "bay-ta" in Britain and "bate-a" in America.

Nobody will correct you for the wrong regional variant. Saying "squiggle" will be noticed.

The alphabet we use came from this one

Greek was adapted from Phoenician around the ninth century BC, and its major innovation was writing vowels as separate letters. The Etruscans took it from the Greeks, the Romans took it from the Etruscans, and the Latin alphabet is the result.

"Alphabet" is simply alpha plus beta.

Common uses

• Reading a formula and wanting to say it aloud.
• Finding a symbol to copy into a document.
• Working out what a letter means in an unfamiliar field.
• Fraternity and sorority names, which are Greek letters throughout.

Questions people ask

How many letters are in the Greek alphabet?

Twenty-four. Sigma has two lowercase forms — ς at the end of a word, σ everywhere else.

What does sigma mean in maths?

Capital Σ means the sum of a series. Lowercase σ is standard deviation in statistics.

Why are omicron and iota rarely used?

Because lowercase omicron is identical to o and iota is too close to i. A symbol you cannot distinguish is useless.

Why did the WHO skip Nu and Xi?

Nu sounds like 'new' and Xi is a common surname. They went to Omicron instead.

Where does our alphabet come from?

Greek was adapted from Phoenician, the Etruscans took it from the Greeks, and the Romans from the Etruscans. 'Alphabet' is alpha plus beta.

Built into the page

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