Fair is foul, and foul is fair' is an example of-

• The Repetition of a consonant at the beginning of two or more words or stressed syllables is called Alliteration.
• Examples of Alliteration:
- 'Puffs, powders, patches, Bibles, billet-doux' is an example of Alliteration.
- Here 'p' has been repeated thrice and 'b' twice.
- Fair is foul, and foul is fair.
- Ruins seize thee, ruthless king!
Source: An ABC of English Literature, Dr M Mofizar Rahman.