Ok, I was writing something yesterday, and grammar correction corrected me. It was putting the article "a" before "strength." For me, "strength" is an uncountable noun, so why does it need "a" before it? I assume it is the concept when nouns are both countable and uncountable. I notice I always make mistakes with them . How can we identify when they are countable or uncountable? (I mean these nouns, which are both)?