This one is tricky both for students and for teachers (to explain) but I see people misuse “decline” and “reduce” in their TOEFL essays all the time. Here’s what you should note:
I can use “reduce” as a transitive verb to mean something like “make smaller”
- The whales reduced the population of sea otters.
- The hunters reduced the population of sea cows.
- To prevent a disaster in my apartment I reduced the amount of clutter.
In this case the subject of the sentence made the following things smaller: the population of sea otters, the population of sea cows, the amount of clutter.
I can’t use “decline” as a transitive verb to mean “make smaller.” I cannot say:
- The whales declined the population of sea otters.
- The hunters declined the population of sea otters.
- I declined the amount of clutter.
When talking about making something smaller, I can only use “decline” as an intransitive verb. Like this:
- The population of sea otters declined.
- The population of sea cows declined.
- The amount of clutter declined.
It isn’t really relevant, but when I use “declined” as a transitive verb it means “refused” or “turned down.” As in:
- I declined the job transfer. (I refused the job offer)