How does the process of rational thinking using buddhi look like?

Question

When buddhi tries to think about something(like solving a problem using logic) does it use the mann to do the thinking part or does the thinking happen in buddhi itself (meaning mann and buddhi work independant of each other while performing rational thinking). So for example, we know one can witness one's mind having vrittis(thoughts). But when one decides to think about something rationally then : Does it happen in the buddhi itself while mann is still doing its thing of creating vrittis and because the person is focused on the rational thinking he ceases to recognise the vrittis occuring in mann OR Does buddhi use the mann to perform rationaly thinking thereby preventing mann from creating any vritti during this time?

In other words : Is mann, the equipment used for performing both kinds of thinking : rational (driven by buddhi)/irrational (mann itself) OR Is buddhi the equipment for rational thinking while mann is the equipment for irrational thoughts (vrittis) ?

TLDR : Buddhi -> creates logical vrittis in the mind -> using such logical vrittis in the mind, buddhi arrives at a logical conclusion -> mind instructs the karmendriyas (action senses) to take action accordingly
OR Buddhi -> creates logical thoughts in itself -> reaches a logical conclusion in itself -> provides logical conclusion to mind -> mind instructs the karmendriyas (action senses) to take action accordingly ?

Answer 1

Source: MIND--ITS MYSTERIES AND CONTROL By SRI SWAMI SIVANANDA

Quoting from the above source:

Manas, Buddhi, Chitta and Ahankara are only Vritti-bhedas or functional aspects of the mind. The Manas has all things for its objects and extends through the past, present and future; it is one only, but has various functions. You are a Judge when you exercise your judicial powers in the court. You are a cook when you work in the kitchen. You are a president of an association when you sit in the chair in that capacity. You are the same man, but you function differently and you are called by different names according to those different functions. Similarly, when the mind does Sankalpa-Vikalpa (will-thought and doubt), it is called Mind; when it discriminates and decides, it is Buddhi; when it self-arrogates, it is Ahankara; when it is the storehouse of Samskaras and seat of memory, it is Chitta; also when it does Dharana and Anusandhana.

While our brain is capable of processing several things at the same time and all of which we may not be conscious, what we consider as a thought is only the conscious mental activity. There can be only one thought at the same instant, but the speed of thoughts are so fast that it may feel like we are multiprocessing. So if we slow down ,focus and observe chitta vritti, as per above reference, it becomes clear that it is the same mind stuff functioning as one of the four functional aspects of the mind, at each instant.

Source:David Godman Book “Be As You are”

Question : What is the nature of the mind?

Ramana Maharshi : The mind is nothing other than the `I’-thought. The mind and the ego are one and the same. The other mental faculties such as the intellect and the memory are only this. Mind [manas], intellect [buddhi], the storehouse of mental tendencies [chittam], and ego [ahamkara]; all these are only the one mind itself. This is like different names being given to a man according to his different functions.

In short, the antahkarana( mind) is in one of the four different functional modes (Manas, Buddhi, Chitta and Ahankara ) depending on the nature of the thought. Antahkarana adorns only one role at a time since only one thought at a time exists in the conscious mind.