Colons and semi-colons, best thought of as lying between a comma (small pause) and a full stop (major pause), have distinct, non-interchangeable functions.
Colons have two major uses:
- to introduce a list (as here)
- to separate two parts of a sentence, the second part explaining or expanding on the first part.
Examples:
- On one side, a trinity is depicted: Diana, Egeria and Virbius.
- Three divinities are depicted: Diana as the goddess of fertility; Egeria as her servants; and Virbius, the woodland god.
- Virgil's choice of Aeneas as hero was judicious: the emperor was believed to be Aeneas's descendant.
- Aeneas is a model of filial piety: he carries his dying father from the burning city of Troy.
Colons should never be followed by a hyphen, and the first word that follows the colon is not capitalised in British English unless capitalised anyway, for example LED, or a proper noun.
Semi-colons have two major uses: to link two complete sentences that are closely related; and to separate items in a list if the items are long.
- Every hero must demonstrate heroic qualities; every hero must struggle with destiny versus desire.
- The first half depicts the fall of Troy; the journey home.
- When marking an project, a tutor looks for a tightly introduction; a detailed argument and discussion; correctly cited evidence; a valid conclusion; and correct spelling, punctuation and grammar.