AbstractThis article proposes a measure of the competitive strength of two rival patterns in the domain of a subgroup of irregular verbs in English. There is competition between simple pasts built on the vowels /æ/ and /ʌ/, and the same competition is found in the domain of past participles. As a result of such competition, the past tensestang(fromsting) was replaced withstung. The /ʌ/ forms are more competitive than the /æ/ forms (Bybee & Slobin 2007,Bybee & Moder 2007). To understand this, we counted the number of types for /æ/ (such assang, rang) and /ʌ/ (such asstung, stuck) in the irregular simple past and did the same in the irregular participle (such assat, hadandsung, done). We calculated a measure of competitiveness for these two patterns incorporating type frequency and token frequency. This measure was used to explain why /ʌ/ forms are more competitive than /æ/ forms.