Is it "a" or "an" in front of Greek letters beginning with a vowel?

Question

Good evening!

I know that it is a basic rule in English that before most vowels, the indefinite particle a becomes an. My question now is: Does this also apply in front of (non-latenized) Greek letters?

For example, is it "a $\omega$-invariant" or "an $\omega$-invariant"?

Answer 1

The rule is whether the pronunciation of the letter name starts with a vowel. So:

• Use an before $\alpha$, $\epsilon$, $\eta$*, $\iota$**, $\omicron$, $\upsilon$, and $\omega$.
• Use $a$ before all other Greek letters.

(* Unless you pronounce it "heta".)

(** Unless you pronounce it "yota".)