Alone of the three TMA distinctions, punctual-nonpunctual correlated with observable phenomena […] Punctual-nonpunctual, however, can be directly observed whenever a single action interrupts a more protracted and repeated one. It could therefore have been grammaticized at a stage when only physical objects or events were capable of being grammaticized or lexicalized. Whether or not grammaticization took place this early, all the evidence suggests that punctual-nonpunctual was the first TMA distinction to be grammaticized, and accordingly, the form that marked the distinction would have been juxtaposed to the main verb.
- Bickerton (1981), a pag.284