"Inflammable" sounds as if it should mean "won't burn". It means the opposite: an inflammable liquid catches fire easily. The word comes from Latin inflammare, "to set on fire", and its in- means "in, into", not "not". People misread it often enough that many safety labels now say "flammable" instead. One prefix, two meanings, and a misreading that matters. Latin prefixes are small, but they decide what a word means.
What a prefix does
A prefix is a piece fastened to the front of a root to change its meaning. The word is itself Latin: praefixus, "fastened in front", from prae- and figere, "to fix". The roots deck in this unit covers the middle of the word (port, spect, duc and the rest). This deck covers the front. Put the two together and you can read words like these:
- trans- (across) + late (carried) = translate, "carried across" into another language
- pro- (forward) + duce (lead) = produce, "lead forth"
- se- (apart) + lect (chosen) = select, "chosen apart"
Prefixes of place and direction
Most Latin prefixes started as words for where something is or which way it moves. Ad- is "toward", ab- is "away from". Ex- is "out of", in- is "into". Sub- is "under", super- is "over". Inter- is "between", intra- is "within", so an international match is played between nations and an intramural one inside a single school.
Some pairs tell a whole story. Ascend (ad + scandere, "to climb") is climbing toward; descend (de + scandere) is climbing down. Export carries goods out; import carries them in.
Prefixes of time and order
Ante- and pre- both mean "before": antecedent, predict. Post- means "after", which is why a P.S. is a postscript, post scriptum, "written after". Re- means "back" or "again" (revert, revise), and retro- means "backward" (retrospect, a look back).
Two prefixes spelled in-
English inherited two different Latin prefixes that look identical:
| in- | Meaning | Examples |
|---|---|---|
| in- (1) | in, into, on | inject, import, inflammable |
| in- (2) | not | invisible, incredible, invaluable |
Invaluable is the second one: something so valuable that no price can be put on it. Not "of no value".
Why ad- turns into ac-, af- and at-
Latin speakers smoothed the join between prefix and root. The last consonant of the prefix often changed to match the next sound. This is called assimilation, and it happened in Latin itself, before English borrowed the words.
- ad-: accept (ad + capere), affix, allocate, attract (ad + trahere)
- in-: impossible, immortal, illegal, irregular
- con-: combine, collect, correct
- sub-: succeed, suffix, support
So a doubled consonant near the start of a word (acc-, aff-, att-, ill-, irr-, coll-, supp-) is often a clue that a prefix has changed shape. The "into" in- assimilates too: illuminate and irrigate don't mean "not" anything.
Greek look-alikes
Greek gave English a second set of prefixes, and some sit very close to the Latin ones:
| Greek | Latin | Shared meaning |
|---|---|---|
| hyper- (hyperactive) | super- (supervise) | over, above |
| hypo- (hypodermic) | sub- (subcutaneous) | under |
| syn-, sym- (sympathy) | con-, com- (compassion) | with |
| peri- (perimeter) | circum- (circumference) | around |
The pair that causes trouble is different: Greek anti- means "against" (antidote, antibiotic), while Latin ante- means "before" (antecedent). Anticipate breaks the pattern: it's Latin anticipare, from ante "before" and capere "to take". The anti- spelling is an old Latin form of ante-, not Greek anti-. Pro- is also in both languages. In produce it's Latin "forward"; in prologue it's Greek "before".
Common mistakes
- Reading every in- as "not". Inflammable and invaluable trip people up. Ask whether "into" or "not" makes sense.
- Mixing up anti- and ante-. Against or before? The meaning of the whole word usually decides.
- Missing a changed prefix. Attract, suffix and correct don't look like ad-, sub- and con- until you know about assimilation.
- Expecting a prefix to explain everything. I'm simplifying when I give one meaning per prefix: de- can mean "down", "away" or simply "completely", and a word's meaning can drift a long way from its parts.
Frequently asked questions
What are the most common Latin prefixes?
Some you will meet constantly are re-, in- (both meanings), de-, ex-, con-, pre-, pro-, sub- and inter-.
Does the prefix in- always mean not?
No. Latin had two prefixes spelled in-: one means "not" (invisible), the other "in, into" (inject, inflammable).
What is the difference between anti- and ante-?
Anti- is Greek and means "against"; ante- is Latin and means "before". Anticipate is the exception that looks Greek but is Latin ante-.
Why do some prefixes change spelling?
Latin changed the prefix's last consonant to match the root's first sound, so ad- + tract became attract and in- + legal became illegal.
Try it
Say each meaning before you flip the card. Then cover the tables: which Latin prefix is hiding in "suppress", and what did it look like before it changed?