Optional.

The optional valency is not necessarily realised in grammatically complete constructions (most of the adverbial modifiers). So the adverbial valency of the verb is mostly optional:

We saw a house (in the distance).

For link-verbs the predicative valency is obligatory:

The reporters seemed pleased.

The obligatory adjuncts of the verb (except for the subject) is called its complements. The optional adjuncts of the verb are called its supplements.

There may be both objective complements and objective supplements; both predicative complements and predicative supplements; both adverbial supplements and adverbial complements:

We did it for you (the addressee is optional).

The night came dark and stormy (the predicative to a notional link-verb is optional).

Mr. X. was staying in the Astoria Hotel (the adverbials of place is obligatory).

Thus

IV) on the basis of the combining power of the verb in relation to other notional words in the utterance notional verbs can be divided into:

1. complementive(those having the power to take complements):