Difference between 愛する and 愛す


How do these two verbs differ?




More or less like "I love you" and "I love thee" differ. 愛す is an older form
with basically the same meaning. Same with other す/する pairs like 略す／略する、座す／座する
etc.




Conjugations of [single-on'yomi-kanji] + する verbs are unstable due to the
lingering influence from Classical Japanese. In short, there are two variants
(五段/consonant-stem and サ変/suru-stem) of the same verb always coexist.

[code]

     愛す       愛する
     愛さない   愛しない
     愛します = 愛します
     愛した   = 愛した
     愛せば     愛すれば
     愛せ       (愛しろ; rare)
     愛そう     愛しよう
     愛せる     (no equivalent)
    
[/code]

(As for imperative, the Classical conjugation 愛せよ is still wide in use as a
bookish expression, but not in everyday language.)

Except those I put in brackets, both series of forms are expected to appear in
the real life, with varied probability. This is applied to all verbs of the
same kind, including 適す（る）, 略す（る）, 制す（る）, 有す（る） etc. Moreover, the probability
which series of conjugation (or even, whose particular form) is used also
differs among verbs; for example, I usually hear the 愛す column used more for
愛, but 制する for 制.

Note that some verbs apparently have similar forms actually don't belong this
type. For example, 楽する looks like another bird of a feather, but it's actually
a colloquial form of 楽をする which is not one solid word, so it doesn't have *楽す
version. The accents are different: らく{LH}する{LH} vs あいする{LHHL}.

