Judgments of which formations of expletive infixation are acceptable are remarkably consistent. This suggests that the rules for the placement of the expletive are not arbitrary, but instead derive from fundamental aspects of
English phonology. A simple rule is that the insertion occurs at a
syllable boundary, usually just before the primary
stressed syllable. A more fundamental theory due to
John McCarthy is based on
prosody. Its basic principle is that "the metrical stress tree of the host is minimally restructured to accommodate the stress tree of the infix". For example, although
unbelievable and
irresponsible have identical stress patterns and the first syllable of each is a separate morpheme, the preferred insertion points are different: ''un-fuckin'-believable
, but irre-fuckin'-sponsible
. McCarthy explains this by saying they have different prosodic structures: un(be((lieva)ble)) but (irre)((sponsi)ble). The infix cannot fall between the syllables ir
and re'' because they form a single
prosodic foot. == Examples in popular culture ==