There are some words which look like the same word but mean different things. Cleave can mean “stick together” or “separate into two or more parts”, for example. And there are other words which look different but mean the same. We’ve already come across “relative” and “relation” on this blog, which have one meaning which is the same, and “spelled” or “spelt”.
This pair is another that lots of people have asked me to write about. I think that most people do know that there’s something funny about them …
Because they mean exactly the same thing. As the Oxford dictionaries define them:
Flammable – easily set on fire
Inflammable – easily set on fire! This one originates from the Latin “in-” prefix meaning into, thereby intensifying the word. Not just easily set on fire; VERY easily set on fire. But I wouldn’t use this one as an intensified version of flammable. They just mean the same.
The word containing the negative or opposite idea, i.e. NOT easily set on fire, is non-flammable.
Oxford prefers the use of flammable, for clarity.
“The label on this nightie says it’s flammable – I’d pick the non-flammable one if I were you, so we can sit together safely in front of the fire.”
You can find more troublesome pairs here.
LibroEditing proofreading, editing, transcription, localisation 
Fohn
August 22, 2011 at 7:33 am
I never really thought about it before! Thanks for the quick lesson. 🙂 Neither ‘Flammable’ or ‘Inflammable’ are in my daily lexicon, but whenever I do approach the prospect of using that phrase, I’ll remember this post. Again, thanks. 🙂
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Liz at Libro
August 22, 2011 at 7:34 am
Thanks for the comment – glad I could help! I think it is one of those where people know there’s something odd, but not quite what …
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Jen
August 23, 2011 at 11:51 am
Do ‘valuable’ and ‘invaluable’ work similarly? Maybe another pair for your list!
And also what about when to use ‘…’ and when to use “…” – I tend to use them interchangeably but maybe I shouldn’t!
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Liz at Libro
August 23, 2011 at 3:51 pm
“invaluable” means extremely useful, so I guess again the intensifier is coming into play. As to quotation marks, it’s fine to use either and in fact different style guides specify different ways round, but I tend to use “” for actual quotations and ” for concepts. The main thing is, if you have to quote someone’s speech in a quotation, use different ones inside and outside the quotation:
Jones states in his article: “The main thing to do is avoid what Peters describes as ‘the errors one commits out of ignorance’ and always check what you’re writing” and this is the main point of my essay.
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