An object complement says what the direct object is, becomes, or is considered to be. In They considered him reliable, him is the direct object and reliable says what they judged him to be.
Two phrases follow the verb. Are they two objects?
The diagram labels her as an indirect object and the keys as a direct object.
The diagram labels him as a direct object and reliable as its object complement.
evidence for the predication
Paraphrase the relation
What does the object complement say about the object?
Reliable is the object complement: it describes the object him.
The paraphrase turns that relation into a whole clause: He is reliable.
A natural be or become paraphrase supports this analysis: They made her a partner becomes She became a partner, while They made her a cake does not say that she became a cake. The paraphrase is evidence, not a word-insertion rule. Tense, result, and wording can change; They named the boat Endeavour needs a fuller rewording.
The diagram labels treasurer as an object complement and shows that this complement is a noun phrase, not an adjective phrase.
Ten sentences from this lesson, one decision at a time.