Whilst there is only one word for more, there are two words for its opposite – fewer and less, and they are sometimes used incorrectly.
Happily this is a very simple error, with a very simple rule to prevent yourself from falling into the trap.
Use fewer when you are talking about things that can be counted. For example:
There are fewer people here than I thought.
He has fewer classes than me this semester.
Use less when you are talking about things that can’t be counted in the traditional way. For example:
I prefer my coffee with a little less milk.
I have less motivation to work than I do to play.
Hopefully if you learn this rule, you will make fewer mistakes, and find yourself less susceptible to making this error!