The apostrophe is the most commonly misused punctuation mark. There are two uses for apostrophes:
- contractions; and
- possessives
Contractions are words where one or more letters have been omitted. The apostrophe is used in place of the letter(s) removed. Some of the most common examples are:
- it’s (it is, it has)
- we’ll (we will, we shall)
- can’t (cannot)
- won’t (will not)
Contractions (it's, we'll, etc.) should not be used in academic essays.
Some words feature an apostrophe because they were once contracted, but now we only ever use the contracted form:
- o’clock
- Hallowe’en
- ne’er-do-well
Possessives indicate that something belongs to someone. The place of the apostrophe depends on whether the possessor is singular or plural. A singular possessive apostrophe goes before the possessive 's'; a plural possessive apostrophe goes after the possessive 's'.
- the catalyst's disadvantages (one catalyst)
- the drug's effects (one drug)
- the crystals' structure (many crystals)
- the drugs' effects (many drugs)
Some people find it useful to think of the singular possessive as:
- the catalyst (its) problem
- the drug (its) effects
and the plural possessive as:
- the crystals (their) problem
- the drugs (their) effects
This helps because, just as the apostrophe in a contraction shows that a letter has been left out, so the apostrophe in possessives shows that the words 'his' 'her' 'its' or 'their' have been left out. In other words, thinking in this way makes it clear that apostrophes always stand in for something that's missing. Understanding this means you'll never get an apostrophe wrong again.
There are some things to look out for: for example, plurals that don't end in 's', e.g. 'children' and 'people', should have the possessive apostrophe placed before the possessive 's'.
- children's bones
- people's assumptions
N. B. the possessive 'its'
The possessive 'its' causes endless confusion with apostrophes. ‘Its’ is the possessive for ‘it’:
- its properties were variable
- its impact was negligible
- its methodology was faulty
- its qualities are debatable
Just remember that like 'his' and 'hers', when 'its' is being used in the possessive sense, it never takes an apostrophe. 'Its' takes an apostrophe only when it's a contraction:
- It's difficult to describe all its uses. (It is difficult to describe all its uses.)
Tips:
1. Plain plurals, i.e. plurals simply denoting more than one, NEVER need apostrophes.
- The chemists showed flair.
- Some polymers are porous.
2. When referencing a multi-author work, e.g. Kernohan et al., phrase your sentence to avoid the possessive 's'. This is because et al. is Latin for 'et alii' which means 'and others'. To mix a Latin abbreviation with English punctuation looks odd, so don't write
- Braunschweig et al's synthesis of a stable oxyboryl complex of platinum.1
instead write
- The synthesis of a stable oxyboryl complex of platinum by Braunschweig et al.'1
The incorrect use of apostrophes shows poor attention to detail, something that no chemist wants to advertise.
1 adapted from Schenk, W. A., Dalton Transactions, 2011, 40, 1209-1219