Why can some words end in either ся or сь? What is the difference?

Question

(Apologies if this question doesn't make sense, I've only been learning Ukrainian for a couple of months.)

I keep seeing words that seem like they can end in either ся or сь and I'm not sure why or what the difference is. For example wictionary lists залишитися (if you open the conjugation table) as having three infinitive forms, "залиши́тися, залиши́тись, залиши́ться" - and then most of the conjugations have two or occasionally three forms but some only have one. What's going on with that? Is it a local dialect variation, or are the meanings different?

Answer 1

What is the difference?

Only one: залиши́тися is a standard dictionary form for the infinitive. So, if you search the word in a dictionary then choose only with -ти(ся) like this.

Is it a local dialect variation?

If you're speaking about things such tests and exams, then there is a standard orthography:

§ 115. Indicative

Rule #9. […]

Note #3: Itʼs always a postfix -ся. But in talking, or writing style you can also use -сь. But if itʼs past time for masculine then -сь can be only after в: усміхну́всь (but стері́гся).

§ 118. Infinitive

Infinitives end with -ти: […].

Note #1: In talking, or writing style you can also use -ть if a base (a part before -ти) of a word ends with vowel: […].

But itʼs kinda yes, because some dialects prefer -ти, and others prefer -ть. The standard language is a mix of dialects; therefore you can use what you prefer. But of course, a dictionary form is the most popular.

If speak about dialects then you can also notice many things, for example some of them:

• for he/she/it removing -ть: [він] залише(ся), or adding -ть: несеть instead current standard несе,
• ся can be separated from verb: ся залишити;
• ся can be writed also as си;
• ть can be writed also as just -т: залишит.

Whatʼs going on with that?

Well… itʼs not so simple but letʼs try.

In some cases itʼs mixing between supin and infinitive.

But mostly itʼs just phonology where:

• removing a vowel but saving palatalizing for consonant: ся − а → сь [я = ьа], ти − и → ть (historicaly и = ьi here) etc; for note, it happens in imperative too: крадь or кради;
• in some cases removing palatalizing: ть → т;
• in some cases и [read ьi] becoming as today и.

Another note

By a rule of orthoepy a part тьсь like in ться is read as long ць, therefore залишиться is залишицця by pronounce.