Possibility / Probability (olabilir, -abilir)

Turkish expresses possibility and probability through two modal forms: the lexical predicate olabilir and the epistemic use of the potential suffix -ebil / -abil. Both forms encode non-assertive modality and indicate that an event is likely, possible, or logically inferred.

1. Function

These constructions mark epistemic modality: the event is evaluated as possible, uncertain, or probable based on available information. They do not express ability in this context, but likelihood.

2. Lexical Predicate: olabilir

olabilir is a lexicalized predicate derived from ol- + -abilir.

It denotes logical or situational possibility.

Examples:
• Hava yağmurlu olabilir. (It may be rainy.)
• Bu doğru olabilir. (This may be true.)

The predicate inflects as a single unit when required:

• olabilir → olabiliriz / olabilirler
• olmayabilir → olmayabiliriz

3. Epistemic Use of -ebil / -abil

The potential suffix -ebil / -abil attaches to verb stems and expresses probability rather than ability when used epistemically.

The interpretation is contextual.

Examples:
• Erken dönebilir. (He/She might return early.)
• Yarın başlayabilir. (It may start tomorrow.)
• Araba bozulabilir. (The car might break down.)
• Ses artabilir. (The sound may increase.)

4. Morphology

4.1. Vowel Harmony

Back vowels → -abilir
Front vowels → -ebilir

Examples:
• al → alabilir
• gör → görebilir
• uç → uçabilir
• dinle → dinleyebilir

4.2. Consonant Alternation (Lexical Patterns Only)

Most stems ending in p, ç, t, k do not undergo softening before -ebilir / -abilir:

• yap → yapabilir
• seç → seçebilir
• bak → bakabilir

Some stems show lexically fixed alternations, especially t → d:

• git → gidebilir
• tat → tadabilir
• et → edebilir

These alternations are lexical, not fully productive.

4.3. Negation

The negative of epistemic possibility is formed with -mA placed before the potential suffix -yAbilir. Here the -bil part stays, and the negative marker comes in front of it.

verb + -ma / -me + -yAbilir

Examples:
• gelmeyebilir (may not come)
• olmayabilir (may not be)
• başlamayabilir (may not start)
• bitmeyebilir (may not finish)

For olabilir: olabilir → olmayabilir (may not be) 

Bu plan olmayabilir. — This plan may not work.

Ability negative drops -bil (gidemem = cannot go). 

Possibility negative keeps -bil and puts the negative before it (gitmeyebilir = might not go).

5. Syntax

Both olabilir and -abilir serve as the main predicate and inflect for person when relevant.

Examples:
• Gidebilirim. (I may go.)
• Gelebiliriz. (We may come.)
• Olabilirler. (They may be.)

No auxiliary verb is required.

6. Distribution and Interpretation

• olabilir expresses logical possibility.
• -abilir expresses contextual or inferred probability.
• Both forms encode epistemic modality rather than ability.
• Negative forms preserve the same modal meaning.