Using "せ" form of する

[Lomaster]

The only way i use it so far is in "negative form + ず" situations, namely せず. What are other common applications of せ form?

 

[Toritoribe]

せ is the 未然形(-nai stem) of a classical verb す, not a conjugation form of する. Similarly, ず is a classiclal auxiliary verb for negation, thus, せず is a remnant of classical Japanese. These kind of classical words still remain often in proverbs or set phrases.
e.g.
義を見てせざるは勇無きなり
～せざるを得ない
～せぬ / ～せん（＝～しない）
～せんとす（＝～しようとする）
～せらる（＝～される passive / honorific)
～せしむ（＝～させる causative)
～せり（＝～した past/perfect tense)

 

[Lomaster]

remnant of classical Japanese

Then no wonder my question arose after hearing a 500 year old vampire speaking. Well, no knowledge is ever wasted i guess. Thanks for the reply!

 

[Mike Cash]

You can still hear some of those even now.