+0
I remember I've been told that "any" could be only used in the Negative Sentences,

but how come it works in this affirmative sentence below,

'Fuel is any substance or material that reacts chemically with another substance or material to produce heat.' ?
+0
This "any" is "it doesn't matter which/who" or "non-specific"
(Ex-1) Take any book you want.
(Ex-2) Any teacher would answer the same.
(Ex-3) Come round any time you like.

paco
Comments  
Teachers: We supply a list of EFL job vacancies
Hi, paco,

Thanks so much for your replying, I really appreciate.
One more question here,
what if I said 'Fuel is SOME substance or material that reacts chemically with another substance or material to produce heat' ? Is it wrong?
When some is used with uncountable nouns, it means either (1) uncertain amount of or (2)certain kind of (not all kind of).
(1) I'd like to have some bread and milk.
(2) Some food is spicy but most is mild.

If you use 'SOME' instead of 'ANY' in the sentence, it sounds like saying "Fuel is a certain kind of fuel" or "Not all of fuel is fuel".

paco