Semi-colons have two major uses.
1. to link two complete sentences that are closely related.
- Hot athenosphere rises beneath the ridge, melting as it rises; this produces magma.
A semi-colon can often be replaced by a comma followed by ‘and’; by putting in a different word like 'but' or 'because'; or by a full stop, with the next phrase beginning a new sentence.
- Hot athenosphere rises beneath the ridge, melting as it rises, and this produces magma.
- Hot athenosphere rises beneath the ridge, melting as it rises. This produces magma.
2. to separate items within a list if those items are long. For example:
- When marking an essay, a tutor looks for a clear introductory paragraph; a sensible structure within paragraphs; a sound argument with appropriate and correctly cited evidence; a measured and valid conclusion; and correct spelling, punctuation and grammar.