ないでもない

ないでもない is a double negative, "it's not that I don't": the speaker admits something, but only partly and without enthusiasm. It follows the ない-form of a verb, and the sentence usually carries on with が or けど to the reservation.

After a noun with が, the ない is "there isn't": 不安がない becomes 不安がないでもない. The two phrases you will meet most are わからないで分からないでもない "I can sort of see it" and きがしないで気がしないでもない "I kind of feel".

ないでもない or なくもない

なくもない means the same and is the more common of the two. It also goes with adjectives, where ないでもない is rare: たかくなく高くなくもない. ないでもない sounds more written; in conversation you also hear a plain まあわかる分かるけど.