Previous research presented Bickerton's 'Bioprogram Hypothesis' as a possible explanation for the preference to mark punctual aspect for past in Singaporean English. The present study examines this explanation in the light of recent grammaticalization studies, and analyzes the relation between past tense marking and the development of counterfactuality implicatures in educated Singaporean English. It is demonstrated that important factors related to diachronic processes in past tense grammaticalization are likely to be significant too in determining the degree of perception of counterfactual implicatures in such varieties.