a or an
'a' precedes words that start with a consonant sound
'an' precedes words that start with a vowel sound
an honorary degree
a or an before acronyms and initialisms
use 'a' or 'an' depending on whether the acronym/initialism begins with a consonant or vowel sound
a UNESCO plan
a GST amount
an ABC show
an ASIO initiative
affect or effect
affect (verb) meaning to act on, to influence or to make a show of
The heat affected the students' concentration.
effect (verb) meaning to make happen or accomplish
It is time to bring a plan into effect.
effect (noun) meaning a result or consequence
The effect of heat on the students' concentration was immense.
amount or number
amount refers to a quantity
An enormous amount of work had to be done before it was finished.
number refers to something that can be counted
Only a small number of people were available for work.
biannual or biennial
biannual meaning twice a year
biennial meaning every two years
bimonthly or semimonthly
bimonthly meaning every two months
semimonthly meaning twice a month
complement or compliment
complement meaning something that completes or makes perfect, the quantity or amount that completes anything
compliment meaning to express praise and admiration
dependant or dependent
dependant (noun) meaning someone who depends on another
dependent (adjective) meaning to depend on something for assistance/support
different from or different to
different from (not different to)
disinterested or uninterested
disinterested meaning free from bias, objective
uninterested meaning not interested
ensure or insure
ensure meaning to make certain
insure meaning to guarantee against risk
fewer or less
use fewer with a plural count noun (referring to numbers)
use less with a singular mass noun (referring to quantity)
forego or forgo
forego meaning to go before
forgo meaning to go without
it's or its
it's is a contraction of 'it is'
It's time to update the website.
its is the possessive of 'it'
The faculty is updating its website.
labour or labor
the Australian Labor Party ('labour' in most other instances)
licence or license
a copyright licence
licensed to sell insurance
practice or practise
it is good practice
to practise law
principal or principle
principal (adjective) meaning first in importance
The principal reason for studying law is to help people.
principal (noun) meaning most important/senior person in an organisation/group
The principal at the local high school has resigned.
principle (noun) meaning a standard of conduct
Jenny has good principles.
stationary or stationery
stationary (adjective) meaning not moving, standing still
stationery (noun) meaning writing materials
than or then
don't use 'then' when 'than' should be used: 'than' is used to compare
Building 1 is bigger than Building 6.
that or which
'that' defines, 'which' informs
This is the house that Jack built.
This house, which Jack built, is falling down.
who or whom
use 'who' if the clause beginning 'who' or 'whom' can turn into 'he', 'she' or 'they'
use 'whom' if it becomes 'him', 'her' or 'them'
you're or your
you're is a contraction of 'you are'
your is belonging to you