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Colons and semi-colons

Be aware of the difference between a colon and a semi-colon.

The examples in this section are taken from The Oxford Book of Modern Science Writing (Dawkins, 2008).

When to use a colon

A colon can be used to introduce a sentence that expands in some way on the previous one, by, for example, providing an explanation, or listing items, as in example (1):

(1) The graph of points for pairs of snapping shrimps always shows a correlation of the sizes of mates: bigger males pair with bigger females, smaller males with smaller females.

When to use a semi-colon

A semi-colon can be used instead of a full stop to separate sentences that are closely connected, as in (2) and (3):

(2) A newborn infant is not a blank page; however, their genes do not seal their fate.

(3) Atoms are assembled into complex molecules; these react, via complex pathways in every cell, and indirectly lead to the entire interconnected structure that makes up a tree, an insect or a human.

Semi-colons can also be used to separate items in a list, especially if the items are quite long, as in (4):

(4) Physical medicine has made significant progress in dealing with the consequences of trauma, illness and disease: it has cured people of terrible diseases such as small pox; it has enabled people to survive following traumatic injuries; and, through transplantation, it has extended the lives of those with failing organs.

(example from Pryjmachuk 2011: 12)

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Dawkins, R. (2008) (ed) The Oxford book of modern science writing. Oxford University Press, pp 34, 41, 60, 88, 363.

Pryjmachuk, S. (2011). Theoretical perspectives in mental health nursing. In S. Pryjmachuk (ed.) Mental Health Nursing: An Evidence-Based Introduction. Sage, 3–41, p 12.