Alliteration

Alliteration is the repetition of the same initial consonant sound in words placed close together, which binds them into a unit the ear hears as belonging together.

The bell in the belfry banged twice and stopped.

Three b sounds in eight words. The repetition welds the phrase together, and the reader hears it as one gesture rather than three separate facts. That binding is what alliteration is for — it is why advertising slogans, band names and children's books are full of it.

It is a sound device, not a spelling one. Cellar and ceiling do not alliterate with cat; phone alliterates with fire.

The line between effective and embarrassing is thin, and it sits at about three. Two alliterating words read as deliberate emphasis. Three read as style. Four read as a tongue-twister, and the reader stops following the sentence and starts counting the letters. That tipping point is where alliteration becomes purple prose.

The bigger practical issue is accidental alliteration, which is a species of mirror words: clean cut clothes, a strange sort of silence. Nothing is wrong, and the ear trips anyway. It is invisible on a silent read and obvious the moment a page is read aloud, which is the only reliable way to catch it.

Its neighbours repeat sounds elsewhere in the word: assonance repeats vowels, consonance repeats consonants that are not at the start.