ABSTRACT
You will perhaps have noticed that byth is used for 'never' when an yn is present in the verb, and erioed is required when a wedi is used. This is a reliable rule with tenses formed with bod + VN. Erioed is associated with completed action (which is what wedi conveys), while byth is associated with ongoing or uncompleted action (which is what yn conveys). But what about the inflected tenses (preterite and short future), where there are no yo's or wedi's to guide us? In fact, exactly the same principle of association applies, so it follows that, with inflected tenses, erioed will be needed with the preterite (past completed action - Basic Welsh, Unit 25), while byth will be needed with the future (action obviously not yet having occurred, therefore uncompleted):
Welwn ni byth mohonyn nhw 'to Weles i erioed y fath beth!
