olemus
modaalsust väljendav verb; nõuete kontekstis väljendab kohustust, keeldu, soovitust või luba

Merriam-Webster:
a verb (such as can, could, shall, should, ought to, will, or would) that is usually used with another verb to express ideas such as possibility, necessity, and permission

ülevaateid
https://en.wikipedia.org/wiki/Modal_verb

https://en.wikipedia.org/wiki/English_modal_verbs

https://www.twinkl.com/teaching-wiki/modal-verb

https://oxfordhousebcn.com/en/4-different-types-of-modal-verbs/

nõuete modaalverbid
- may
- must
- must not
- shall
- shall not
- should