I'm confused over when the word "difficulty" is countable and when it's uncountable. Please help if you can.
According to the First Certificate textbook I'm using, both of these sentences are correct:
He had great difficulty in understanding the instructions.
He had great difficulties in understanding the instructions.
But the same textbook says that only the FIRST of these sentences is correct:
Many people have some difficulty learning English.
Many people have some difficulties learning English.
I'm having great trouble explaining why the sentence in red is wrong.
Difficulty - Uncountable
This is when you talk about the state of something being difficult to do/understand/etc.
Difficulty - Countable
This is when you are talking about the 'problems'
I had difficulty reading the book (the text was really difficult to understand)
I had difficulties reading the book (first, I couldn't get a copy of it; then I left it at school and someone else took it. I finally got another copy but half of the pages were missing.)
I hope this helps.