Conjugating Nidan Verbs


I am studying elementary Japanese, not classical forms of the language. In the
online dictionary Jisho.org, I found the verb 憂ふ/'to be worried or concerned
about' listed as a nidan verb. Does that mean that the verb must be
used/conjugated in classical Japanese, that it would now be integrated as an
ichidan verb, or that it is completely archaic and would not be used at all
now?




Yes 憂ふ is basically a verb in classical Japanese written with [historical kana
orthography](https://en.wikipedia.org/wiki/Historical_kana_orthography). FWIW,
No verb in modern Japanese ends with ふ. The modern equivalent of this verb is
[憂える](https://jisho.org/word/%E6%86%82%E3%81%88%E3%82%8B).

That being said, since this is a literary verb, the classical version is
somethimes used today using the modern kana orthography (憂う). For example,
憂える声 and 憂う声 are both used ("voice of concern"). The former is theoretically
correct but the latter is preferred by many. Practically speaking, you should
be using the modern version when you want to conjugate freely or stick to the
standard (憂えている, 憂えた, ...), but as an exception, you may use unconjugated 憂う
at the end of a sentence or a relative clause.

  * [「憂う」と「憂える」](https://mainichi-kotoba.jp/photo-20161128)
  * [規範と違う「憂う声」が多数派](https://mainichi-kotoba.jp/enq-143)




Yes 憂ふ is basically a verb in classical Japanese written with [historical kana
orthography](https://en.wikipedia.org/wiki/Historical_kana_orthography). FWIW,
No verb in modern Japanese ends with ふ. The modern equivalent of this verb is
[憂える](https://jisho.org/word/%E6%86%82%E3%81%88%E3%82%8B).

That being said, since this is a literary verb, the classical version is
somethimes used today using the modern kana orthography (憂う). For example,
憂える声 and 憂う声 are both used ("voice of concern"). The former is theoretically
correct but the latter is preferred by many. Practically speaking, you should
be using the modern version when you want to conjugate freely or stick to the
standard (憂えている, 憂えた, ...), but as an exception, you may use unconjugated 憂う
at the end of a sentence or a relative clause.

  * [「憂う」と「憂える」](https://mainichi-kotoba.jp/photo-20161128)
  * [規範と違う「憂う声」が多数派](https://mainichi-kotoba.jp/enq-143)

