Search BBC
BBC World Service
BBC BBC News BBC Sport BBC Weather BBC World Service Worldservice languages
spacer gif
You are in: Learning English > Grammar and Vocabulary > Learn It!
Learning English
spacer gif
learn it! title
 'Flammable' or 'inflammable'? Negative prefixes, un-, in-, im-, il-, dis-, etc.
fire extinguisher
Garnet Teo from Singapore asks:

what is the difference please between flammable and inflammable?
Roger replies:more questions

There is no difference in meaning and little or no difference in use.
Chemicals, gases or cloth materials that are flammable / inflammable catch fire and burn easily. Perhaps, in usage, cloth materials are usually described as inflammable. So we might say: 'The material from which these car seats are made is highly inflammable. And conversely, certain gases or chemicals may be thought of as flammable. So we might say: 'Aircraft fuel is highly flammable'. But there are no hard and fast patterns.

All this is somewhat strange, because usually when we add a prefix such as in- or un- or dis- to the beginning of adjectives, adverbs and verbs, we give them the opposite meaning.

Try this activity. Draw half a dozen columns on a large piece of paper and insert a prefix heading in each column. Perhaps leave one or two columns empty for new prefix headings as they occur to you. Your piece of paper should look something like this:

Then, over a period of time, write in as many adjectives with a negative meaning using these prefixes that you can think of.

To help you get started, you might like to test your knowledge against these opposites. Print out this exercise, fill in the missing words and then check your answers against the answer key. The first one is done for you.

Opposite of:

happy:   We were really unhappy with the way the party was going
  1. legal: There is no doubt that cannabis will remain an ______________ drug for the foreseeable future.
  2. possible: It was quite _________________ for us to drive all the way from Paris to Madrid in one day.
  3. successful: He made an ________________ attempt to climb the highest mountain in the range.
  4. responsible: To take the boat out with four children under the age of ten and with no life jackets on board was quite ________________ of him.
  5. appropriate: The dress she was wearing was quite _________________ for the occasion.
  6. polite: It was very ________________ of him to insult his mother in front of his aunt.
  7. religious: They were a completely _________________ family and I never thought that one day I would marry one of the daughters.
  8. honest: As a politician he was __________________ and it was not long before nobody trusted him.
  9. perfect: The goods were ________________ and had to be returned to the store we bought them from.
  10. contented: She was __________________ with her life and decided that things had to change.











1. An illegal drug
2. Impossible to drive such a distance in one day
3. An unsuccessful attempt
4. Irresponsible behaviour
5. A dress which was inappropriate for the occasion
6. Impolite behaviour
7. An irreligious family
8. A dishonest politician
9. Imperfect goods
10. Discontented with her life

N.B. As you complete your table, you will probably find that you end up with many more adjectives in the un- and in- columns than in any others. Happy hunting!

BBC copyright
Learning English | News English | Business English | Watch and Listen
Grammar and Vocabulary | Communicate | Quizzes | For teachers
Downloads | FAQ | Contact us