Necessity means that the state or fact described by the proposition must be or must occur.
That necessity may be due to:
- factors internal to the agent and directly felt by the agent himself, it is then a need,
- objective external factors, resulting from the outer world, for objective necessity,
- an outer authority, more or less personal, it is then an obligation.
Necessity may be more or less strong or imperative, from nice to have to mandatory.

● The nominal construction "verb-ISHI KERAK", i.e. the infinitive suffixed with the possessive type of personal suffix, and followed by the nominal predicate kerak ('necessary'), is the main form used to express necessity, be it an internal need, an objective necessity or an obligation.
Instead of kerak, the nominals lozim and zarur may be used with the same meaning, but with a more literary flavour.
To express a necessity which applies to anybody or anything, the personal suffix is not used.

- Internal need:

Mahalliy xalqlar tilisini bilishim kerak.
We need to know the local language.

Lekin biz unutmasligimiz kerak.
But we need not forget.

- Objective necessity, of general application:

Shoshilish kerak emas.
There is no need to hurry.

Qo'ng'iroqni chalish kerak!
One must ring the bell.

- Objective necessity, for a specific person or fact:

Bir soat kutishingiz kerak.
You have to wait one hour.

Bir soat kutishingiz kerak bo'ladi.
It will be necessary for you to wait for an hour.

Bu masala tez hal qilinishi lozim.
This problem must be resolved quickly.

- General obligation:

Yo'l bermaslik kerak.
It must not be allowed.

To'lash kerak bo'ladi.
It will be necessary to pay.

- Specific obligation:

Siz meni kutishingiz kerak.
You must wait for me.

Kechgacha ishxonada bo'lishim kerak.
I will need to be at the office until late.

- The basic meaning of kerak and lozim is 'to be a need for somebody', making use of the nominal construction "noun-GA KERAK", i.e. the noun representing the person needing a thing in the dative, and then followed by kerak (or lozim).

Sizga nima kerak?
What do you need?

Oliy o'quv yurtiga kirish uchun yetuklik attestati kerak.
You need a school-leaving certificate to enter a high school.

Bu kitob o'zimga lozim.
I need this book myself.

- The basic meaning of the construction "verb-ISHI KERAK EDI" is to express a past necessity:

U xat yozishi kerak edi.
He had to write a letter.

Men kelishim kerak edi.
I should have come.

Sovet davriga Markazga faqat paxta kerak edi.
During the Soviet era, all that the Center needed was cotton.

- Performative modality: A derived meaning of kerak edi is to weaken the imperativity of a demand, making it more polite:

Bo'sh xonangiz bormi?
Ha, bor.
Bir kishilik xona kerak edi.

Have you got rooms?
Yes, we have.
I would need a room for one person.

● Other constructions expressing internal need are:
- "verb-ISHGA MUHTOJ" (or "noun-GA MUHTOJ"), followed by the pronominal type of personal suffix,
- "verb-ISHINING HOJATI BOR/YO'Q"; i.e. the infinitive suffixed by the possessive type of personal suffix, used in the nominal genitive construction with the head noun hojat ('need', 'necessity'), itself suffixed with the possessive third person, the existence or non-existence of that need being predicated by bor or yo'q.
The need expressed in these constructions may be slightly more imperative than with kerak.

Men sening yordamingga muhtojman.
I need your assistance.

Men pulga muhtojman.
I need money.

Bu yerga kelishingizning hojati yo'q.
There is no need for you to come here.

● The modal noun SHART is the most emphatic of the words expressing objective necessity or obligation.
The construction is the same as the one found in "verb-ISHI KERAK".

Majlisga kelishingiz shart emas.
You are not obliged to go to the meeting.

● A construction expressing a weaker necessity is:
- "verb-ISHGA TO'G'RI KEL-", ('it comes right that...') conjugated at any tense needed.

Ko'p ishlashga to'g'ri keldi.
A lot of work had to be done.

● Another construction expressing obligation is:
- "verb-ISHGA MAJBUR", followed by the pronominal type of personal suffix.

Ketishga majburdirsiz.
You really have to go.

Men shu soatning ichida jo'nashga majburman.
I have to leave within one hour.

Bu shahardan chiqib ketishga majbur bo'ldim.
I was forced to leave the city.

● Factitives ('make somebody/something do/be') can be applied to those modalities, giving derived meanings such as forcing, obliging.

- Compelling, forcing: "verb-ISHGA MAJBUR QIL-", "verb-ISHGA ZO'RLA-".

Sharoit meni rejamni o'zgartirishga majbur qildi.
The circumstances forced me to change my plan.

Sizni hech narsa kelishga majbur qilmaydi.
Nothing obliges you to come.

Ota o'g'lini o'qishga zo'rladi.
The father forced his son to study.