Turkish: A Comprehensive Grammar

(v) Assumptive use of olması gerek/lazım:
The construction -mA-POSS gerek/lazım is one of the means of expressing objective
necessity, as explained in 21.4.2.2. The 3rd person form with the copular/auxiliary ol- as
the verb can have the secondary function of expressing a strong assumption based upon
knowledge of other relevant facts. The time reference is either present or, where there is a
preceding verb form with -mIş, past:
(85) Bu saatte [Ali’nin işte olması] lazım.
‘Ali must be at work at this hour.’ (I know his hours of work.)
(86) [Herkesin afişi görmüş olması] gerek.
‘Everyone must have seen the notice.’ (It was in an obvious place.)
(vi) Deductions with olmalı:
The obligative form (see below, 21.4.2.2) of the copular/auxiliary verb ol-expresses an
inference drawn about a past or present event or state from strong circumstantial
evidence. In nominal sentences the time reference is present tense:
(87) Kapı açık, evde olmalılar.
‘The door’s open; they must be at home.’
For the use of olmalı following the -mIş or -(I)yor form of another verb, see 21.5.1–2.
21.4.2 POSSIBILITY AND NECESSITY
The concepts of possibility and necessity differ from other types of modality in having
objective components that are independent of the speaker’s perception or attitude. Ahmet
can swim two kilometres and The card has to be inserted slowly are examples
respectively of objective possibility and objective necessity.
21.4.2.1 The expression of possibility
The suffixes which mark possibility and impossibility are the verbal suffixes -(y)Abil and
-(y)AmA (the latter incorporating the negative marker -mA). The markers of possibility
and impossibility enter into a wide range of combinations with the markers of tense,
aspect, and other types of modality. Non-finite verb forms can also be marked for
(im)possibility:
(88) konuş-abil-mek
talk-PSB-VN
‘to be able to talk’
(89) gör-e-me-yen-ler
see-PSB-NEG-PART-PL
‘those unable to see’
Where -(y)Abil is added to the negative stem of a verb, it denotes the possibility of the
action not occurring, or the freedom of the subject not to perform it:
(90) söyle-me-yebil-mek
Turkish: A comprehensive grammar 300