This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 7 was part of a daily 30-minute discussion on the suttas, the Dhamma talk and reflections.
Slightly edited to improve readability
(Question is referring to MN 148, the Chachakka Sutta.)
Thoughts are part of the mind. The mind is part of the six sense bases, so thoughts should be considered to be one of the six senses, one of the six feelings, if you will. That means that it is arisen due to dependent origination. At the level of contact, so if you have contact with something, you might have a thought about it. That thought arises through the process of perception, where the contact activated a formation that could create a consciousness, that then drives forward the idea of that thought. That’s the perceiving aspect of the thought, that it recognizes for example that’s what it is. Or if you’re having thoughts about the past, that can also happen due to contact with one of the five physical senses, or due to reflection and thinking. This is again initiated by the process of formations. Even thoughts of the future are initiated from within, meaning through the process of formations. All thoughts, whether they’re of the present moment, the present condition, or past, or future are arisen through formations. And those formations are conditioned by the contact that arises.
If you have a feeling, or there is a contact, which creates multi-sensory experiences. Let’s say you smell a fragrance, and it reminds you of something that happened in your past. The experience of that smell then activates the formations, that continue to create the perception that’s rooted in the memory. And then that creates mental proliferation in the way of reflecting on that smell, then that thought leads to another thought, and that thought leads to another thought and so on and so forth. So, all these thoughts can arise after contact. It’s only after contact the thought would arise. The contact can be through any of the five physical senses, or through mental objects in the mind as well.
[Follow up question]
Can contacts from the five senses cause more thoughts to arise?
It has been the experience of some people where there’s a lot of sounds in the background and it starts to create different kinds of thoughts about it. And then that can create more and more thoughts. But that depends upon the person’s awareness or their mindfulness. So as soon as they recognize that they’re starting to sway away and get carried away with their thoughts, as soon as they see that mental proliferation is arising, then they can recognize it and let it go. So, it is possible that the multi-sensory experiences, the different experiences of the five physical senses can create multiple thoughts as well.