So I am writing my paper and I am confused I know you use fewer when you have something countable like items. and less when its not a countable things. For my example would I say that 5% concentration of coffee had less of an effect of fewer effects than a 10% concentration of coffee . thanks

I would use "less of an effect" -- unless you have named different effects separately.

Okay, Thanks!

You're welcome.

Great question! You're on the right track with the usage of "less" and "fewer." "Fewer" is used when referring to countable nouns, like items or things that can be individually counted. "Less" is used when referring to non-countable nouns, such as substances or qualities that cannot be easily quantified.

In your example, you are talking about the effects of coffee concentrations, which are not countable items but rather a non-countable quality. Therefore, you would use "less of an effect" instead of "fewer effects."

So the correct sentence would be: "A 5% concentration of coffee had less of an effect than a 10% concentration of coffee."

Remember, when in doubt, think about whether the noun can be counted individually or if it represents a non-countable quality, and then choose "fewer" or "less" accordingly.