決して～ない　vs　まったく～ない


What is the difference between **決して～ない** and **まったく～ない**?




There's definitely an overlap in the "completely/absolute" domain between
決して...ない and まったく...ない

If we want to split them apart, then Chocolate has a good pair of sentences to
help illustrate the difference:

> 「決して忘れません」

= _definitely_ don't forget.

決して usually relates to volition or decisional completeness / finality.

Or the opposite of not being committed to remembering.

Command-related usage is quite common for 決して so it also has a kind of
[必ず](https://kotobank.jp/word/%E6%B1%BA%E3%81%97%E3%81%A6-489955) sense.

> 「全くわかりません」

=I don't understand _at all_

Or we could say there's nothing in the contents I understand (the opposite of
understanding all of the contents).

まったく relates to completeness of things.

* * *

A further signal other than looking at usage that tells us 決して is more formal
is that 決して depends on the 音読み of [決](https://kakijun.jp/page/07136200.html)
whereas まったく when written in kanji uses one of the 訓読み of 全.

