An absence of common sense or reasonableness, as in This memo has no rhyme or reason. Closely related variants are without rhyme or reason, as in The conclusion of her paper was without rhyme or reason, and neither rhyme nor reason, as in Neither rhyme nor reason will explain that lawyer's objections. This term originated in French about 1475 and began to be used in English about a century later. Sir Thomas More is credited with saying of a mediocre book that a friend had put into verse, “Now it is somewhat, for now it is rhyme; whereas before it was neither rhyme nor reason.”
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.