Reasoning doesn’t seem to be a choice, it seems to just happen.
What does happen, and how?
I am walking along the road on the sidewalk. I know this setting, walking it every day.
Then I sense (eyes) a small rectangular dark object ahead on the sidewalk.
The object now in my thoughts (delivered by my brain from my eyes) is new.
Being new, not known, my will is prompted by my intellect to desire with the understanding that “It would be good to know what it is”
My will then moves my appetite for sensitive cognizance to move my feet to walk toward it, my back to stoop over, my eyes to focus to the correct aperture, etc. When at the point where I can make out its detail, my appetite for cognizance is satisfied and I stop,
My eyes read “SNICKERS” on the rectangular object, and now the object in my thoughts is a Snickers bar.
I know “what it is” in my intellect. I know it is good to be united to it (in my mouth) in my rational thought. and my appetite for food, attentive to my reason, desires what is good to eat. It does not choose to desire. It simply and mindlessly desires what the reason knows is good to eat. The understanding knows “What it is”, the reason declares “It is Good (or not)” automatically. And the appetite desires (moves the hand to reach for it). The understanding of What is a separate activity, as is the reasoning of goodness, as is the appetitive desire (therefore bodily movement) of union with goodness.
Then, my intellective reason, desires to know the whole reality. This is the beginning of “moral decision”. Why is a candy bar lying on the sidewalk. Speculative reason begins reasoning through possibilities that will make sense, so that the intellect will be satisfied with the big picture of the truth of a candy bar on the sidewalk. “Phantasms” of possible reasons are formed in the brain - someone walking along dropped it; someone poisoned it and left it there to hurt another person, etc.
With each image, various sensitive appetites are triggered to look around with the eyes and bodily turning, etc. They are triggered by the reasoned understanding of the relative goodness or badness of the phantasms’ contents. They also are moved by the will to hesitate reaching for the candy bar. Desirability is now tempered by a new uncertainty in the reason concerning goodness to eat.
At some point, the reason, not the will, comes to a conclusion - “Yes, this would be good to eat and safety concerns are minimal and no one is coming back to look for a lost Snickers bar so it is not stealing” (that last one is a questionable assumption - I would go back to find one that I dropped).
With this decision of goodness, the will desires and removes the caution flags from the sensitive appetites, such that they move the body to satisfaction.