I think I have asked this before elsewhere, but haven't figured it out yet. Sorry if it's been asked already in the archives, I didn't have a look.
Are thoughts vipaka? If I'm not mistaken, mental objects are included as external ayatanas the way forms, sounds, tastes etc are. But are these mental objects thoughts, or something much more ephemeral, or are thoughts a kind of active by-product that comes about as proliferation etc in response to risen objects? I hope that question is clear.
When we wake up, first thing in the morning, it feels as if there are thoughts that come out of nowhere, that arise as a resultant of the previous days thinking, for example. And it feels like those thoughts are vipaka. But I would guess that the correct answer is that thoughts are conceptual and therefore are not dhammas, and cannot be vipaka. Mental objects that are external ayatanas must be something far more fleeting than thoughts. Right?
Kammalakkhano , bhikkhave, bālo, kammalakkhano pandito, apadānasobhanī paññāti
(The fool is characterized by his/her actions/the wise one is characterized by his/her actions/Wisdom shines forth in behaviour.)
(AN 3.2 Lakkhana Sutta)