Alliteration is front rhyme. The initial syllables rhyme, as in “fancy feet,” instead of the final syllables, as in “neat feet.” Consonants alliterate only with themselves (“faulty feet”), while any vowel can alliterate with any other vowel (“itching arches”).
We’re talking about sounds, not letters. So “happy herbs” does not alliterate (in American English, anyway), but ”erotic herbs” does. “Pneumatic knees” alliterates, but “persistent pneumonia” does not.
Alliteration links words together, creating extra meanings. It makes phrases jump off the screen, and can cement them into the readers’ memory, as in “Frosted Flakes.”
It works unless it’s overdone, as in William Safire’s famous phrase coined for Vice President Spiro Agnew: “nattering nabobs of negativism.” In stretching for two words to alliterate with “negativism,” Safire nosedived archly into archaic nonsense.
Sometimes, alliteration gets out of control, as in this passage from Amanda McKittrick Ros, describing her villain, Madame Pear, who “had a swell staff of sweet-faced helpers swathed in stratagem, whose members and garments glowed with the lust of the loose, sparkled with the tears of the tortured, shone with the sunlight of bribery, dangled with the diamonds of distrust, slashed with sapphires of scandals.” There’s a reason why The Oxford Companion to Irish Literature described her as “the greatest bad writer who ever lived.”
Here’s a sentence I wish I had written, by Adam Nicolson, in his Seize the Fire: “The ship was a place of yelling, the guns roaring, the blocks and tackles with which they were hauled out through the gunports and manoeuvred to bear on the enemy, screaming and squealing like pigs on the point of slaughter.” Nicolson alliterates “screaming” and “squealing” and “slaughter,“ tying those terrifying words together; and they in turn frame “pigs” and “point.” Lord Nelson’s enemies didn’t stand a chance.
[Ever used alliteration as an interesting and inventive artifice?]