We can break many English words into parts, called affixes (these are prefixes or suffixes) and root (base) words. The affixes change or add to the meaning of the root word.

Prefixes go in front of root words, and suffixes go behind. There are hundreds of prefixes and suffixes in English.

Example: un (prefix) + happy (root word) + ness (suffix) = unhappiness

To understand how prefixes and suffixes work, it is useful to understand something about root words:

Root words sometimes can stand alone (examples: judge, appear, play – or happy, as in the example above)

But sometimes these roots aren’t proper words on their own and need a prefix or suffix to have meaning. Eg the word transmit – the prefix is trans, and the root word is mit. – Mit isn’t a word on its own.

These root words with no meaning often came from Latin or Greek or French originally, for example mit meant meant ‘send’ in Latin. (And the prefix trans also comes from Latin, meaning ‘across’.)

Here, we’ll focus on prefixes, many of which also come from other languages, such as Latin, Greek or French. (The next chapter will deal with suffixes.)

‘Pre’ – before. So, the definition of ‘prefix’ is: a meaningful group of letters that attach to the beginning of a root word and create a new word.

Here are some more examples of words that are prefixed with ‘pre’:
precede (go before),
predated (happened before something else),
premature (too early).
Can you think of others?

While there are many prefixes, here are four very common ones:
Dis – not. Examples: disqualify (not qualify), disown (no longer have connection with)
Un – not. Examples: unhappy (not happy), uncover (remove a cover/not cover)
In – in OR not. Examples: income (money coming in), inconvenient (not convenient/causing difficulty)
Re – again. Examples: redo (do it again), recover (get better again)

Did you notice that three of the four prefixes in the table above have a negative meaning?

And did you notice that the prefix ‘in’ had two meanings – in and not? This can sometimes be confusing!

Here are four more commonly used prefixes that also change a word from a positive meaning to a negative meaning:
im + patient = impatient (not patient) [Note: The prefix ‘im-’ is usually followed by ‘b’, ‘m’ or ‘p’: impossible, imbalanced, immature]
il + logical = illogical (not logical)
ir + relevant = irrelevant (not relevant)
non + sense = nonsense (not meaningful)

Here are some other common prefixes. If you know them then it can help you work out what words mean.
Anti – against. Examples: antibiotic; anticlockwise
Auto – self. Examples: automatic; autobiography
bi – two. Examples: bicycle; bifocals
circum – around. Examples: circumstances; circumference
co – with/together. Examples: co-author; cohabit
con, com – with/together. Examples: connect; coincide
contra, contro – against. Examples: contradict; controversial
counter – against. Examples: counteract; counterattack
de – down, off, away from. Examples: degrade; deactivate
en, em– cause. Examples: to enact; empower
ex – out of/previous/from. Examples: extract; ex-student
extra – beyond/more than/outside of. Examples: extracurricular; extreme
fore – before/front of. Examples: forefathers; forefront
hyper – more/beyond. Examples: hyperactive; hyperallergic
inter – between/among. Examples: internet; international
mal – bad. Examples: malnourished; malfunction
micro– very small. Examples: microorganism; microscope
mid – middle. Examples: midway; midsection
mis – wrongly. Examples: mistake; misunderstand
multi – many. Examples: multicoloured; multinational
over – too much. Examples: overjoyed; overcome
post – after. Examples: postpone; postgraduate
pro – forward. Examples: promote; progress
quad – four. Examples: quadrangle; quadrant
semi – half. Examples: partly; not fully semi-circle; semi-final
sub – under. Examples: substandard; submarine
super – above. Examples: superhuman; supervise
trans – across. Examples:  transmit; translate
tri – three. Examples: triangle; triathlon
under – under/too little. Examples: underfoot; underachieve
uni – one. Examples: universe; unicorn

The same root word may have different prefixes, for example: construct (build), destruct (break down), instruct (teach), obstruct (get in the way). Notice how the prefix changes the meaning completely each time.

Prefixes often attach to root words that have a suffix. You saw an example earlier: unhappiness. More examples: underachievement; transmission; internationalism; extremely; promotion; supervisory.