Potential and Causative form clarification - 倒せる / 倒せない

Question

Hopefully this is a nice easy one, but it's something I need clarification on. So I have a sentence here, using (I think) -せる form. (倒せない)

アイテムを使わないと倒せない敵もいるが、戦いの基本はやはり剣だ。

My question is a general one - what does it mean when -せる form is used?

倒しません、　倒さない、　倒せない these are all the same meaning aren't they? Or not?

Answer 1

I don't know what you mean by "-せる" form.

-せる can appear at the end of the verb in at least two ways.

• As the potential form of a verb, which ends in -す. 帰す -> 帰せる
• As the causative form of a verb. 帰る -> 帰らせる

Here, -せる is the potential form of the verb 倒す, so

倒す "to throw over, to knock down"
倒せる "to be able to throw over / knock down"
倒せない "not to be able to throw over / knock down"

by which you get

倒しません e.g. I don't throw it over (polite)
倒さない e.g. I don't throw it over (informal)
倒せません e.g. I can't throw it over (polite)
倒せない e.g. I can't throw it over (informal)