What is the difference between alliteration, assonance, and consonance?
All deal with repetition of sounds within words, phrases, and sentences. The differences are what is repeated and where the repetitions are located.
There are many different ways someone can use the repetition of sound within a word or sentence to add flow, rhythm, rhyme, and even a bit of musicality to their language. It's this musicality of language that is what distinguishes poetry from prose.
One way someone can do this is to put the same sound at the beginning of some, or even all, words within a sentence. Such as:
"Amy's apples are awful."
"Gerry's grapes are great!"
These are examples of alliteration.
But "Charley's cherries are cold" is not alliteration - alliteration is based on sounds and not letters of the alphabet.
The use of a series of consonants in quick succession is another way to achieve a poetic effect, such as:
"The pitter patter of perpetual precipitation put me in a petulant mood".
While there is alliteration in this sentence with the letter p being repeated in the beginning of words, the repeated p and t are consonant.
The same can be done with vowels, and this is called assonance, such as:
"When the wren cries and the time sublime, the breeze in the tree will wend many a line."