Instead, the object of the verb “know” is a whole clause, “he will prevail.” That’s why this sentence uses the subject form in “he.” Without “will prevail” it would be different.

Whenever the compound is the subject of a clause, then you want I. For example: Tom and I enjoy pizza. In this sentence, the Tom and I are performing the action: enjoying.

A 1998 edition of the Websters New World Dictionary. Matching subject and verb when inverting statements into questions can get complicated, writes June Casagrande.

Learn and revise sentence types and clauses, nouns, adjectives and verbs with this BBC Bitesize GCSE English Language (AQA) study guide.

Learn and revise sentence types and clauses, nouns, adjectives and verbs with this BBC Bitesize GCSE English Language (Eduqas) study guide.