Consonance and assonance are poetic forms that are similar in that they both feature similar sounds being repeated throughout a single line of poetry. The difference between consonance and assonance has to do with the type of repeating sounds found in the line. Assonance occurs when vowel sounds are repeated several times within a line, while consonance features repetitive consonant sounds throughout, usually in the middle or end of words. Using these techniques can help a poet add subconscious meaning to the words of his poem through the effect that the similar sounds have on the reader or listener.
Many people think of poetic devices only in terms of what the words of the poem mean. For example, a poet can use techniques like metaphor or simile to extract more than the literal meaning of the words on the page. There are also devices by which poets can create effects based on the sound of the words in their poems. Two of these devices, consonance and assonance, are achieved through different means but often have the same intent. They are both used to add meaning to the words of the poem from the way they sound when spoken.
One basic difference between the two forms can be found in the sounds with which each device is associated. In the case of assonance, those sounds are rhyming vowel sounds that occur in several words within a line. The words themselves do not necessarily have to rhyme with each other, but the vowel sounds need to be similar. For example, the line, "The rain laid waste to the graves" contains assonance through the repetition of the long "a" vowel sound four times.
By contrast, consonance repeats consonant sounds several times throughout a line. When this occurs at the start of words, as in the phrase "furiously fighting with fists," it is known as a separate technique called alliteration. Consonance exists when consonant sounds are repeated in the middle or at the end of words in a line. One example of consonance would be the line, "In the middle of the puddle he waddled."
There are many ways that poets can use consonance and assonance to add extra dimension to their poetry. The sound of the words can actually emphasize the meaning of the words. In addition, using these techniques in an extreme manner can often add a hint of humor to a poem. No matter the intent, the effect created by the way that the words sound when spoken together is the reason that poets use consonance and assonance so often.