Instrumental singular declension ба́ня: -ей, why could it also be -ею?

Question

I'm learning declension charts for Russian nouns.

Wikipedia shows the first declension chart as follows:

	Singular			Plural
Nominative	-а	-я	-ия	-ы	-и	-ии
Accusative	-у	-ю	-ию	-ы/–	-и/-ь	-ии/-ий
Genitive	-ы	-и	-ии	–	-ь	-ий
Prepositional	-е	-е	-ии	-ах	-ях	-иях
Dative	-е	-е	-ии	-ам	-ям	-иям
Instrumental	-ой	-ей	-ией	-ами	-ями	-иями

Wiktionary gives the declension for ба́ня, where the singular instrumental singular apparently has two options: ба́нею and ба́ней. This happens for other words as well (e.g. рабо́та: рабо́той/рабо́тою).

Why do the two alternatives show up on Wiktionary? Why does Wikipedia only show one? When is it appropriate to say банею instead of баней?.

Answer 1

Those are stylistic variations of the same ending which exist for first declension nouns (баней/банею), third declension feminine nouns (вещью/вещию) and feminine adjectives (полной/полною).

The ones with the elided vowel are neutral, the ones with the full vowel are archaic or grand style.

The shorter ones are the natural result of tendency towards reduction in unstressed vowels in Russian. They haven't completely supplanted the full ones because of Church Slavonic influence. In Church Slavonic, the literary language of old, vowel reduction was not a thing, so using the full form would give your discourse the bookish feel.

Answer 2

"When is it appropriate to say банею instead of баней?"

You'd better not. We usually use -ой, and -eй. And not only with nouns, ending with -а, -я, ( мама -— мамой, дядя — дядей) but also with adjectives (красной, синей) and pronouns as well ( своей сестрой, со мной, с тобой, с каждой минутой).

But you will find a lot of of -ою, and -ею in songs, poetry, folklore.

Под сосною зеленою спать положите вы меня.... Калинка, калинка...

Я не понимаю, что со мною, со мною, со мною. Возможно, это связано с тобою, возможно, или нет.

Жил старик со своею старухой у самого синего моря. А. Пушкин.

Чародейкою Зимою

Околдован, лес стоит -

И под снежной бахромою,

Неподвижною, немою,

Чудной жизнью он блестит.

Ф.Тютчев