Explanation must be distinguished from justification.
Statements
Explanation -- a causal explanation of why something happened (i.e. why did Jason kiss Stella? His DNA is programmed to secrete high levels of dopamine when he sees a biological female ...)
Justification -- what were the reasons going through Jason's head when he decided to kiss Stella? If he had sufficient reasons for kissing her (i.e. I like her, I l think she is into me, we only live once)
The paragraph explains how these two things sometimes overlap, sometimes don't.
conditional (only when = put it on the right)
Justified → person has sufficient reasons action for the action
(only = put it on the right)
Rational → the justification (reasons) action for the action are an essential part of explanation
Evaluate
This is a tough read. I understood it to be referring to the classic Mind / Body problem. Do we have free will? Do we get to choose, based on our rational reasoning, which actions to perform? Or are our actions explained by a bunch of biochemical reactions in our brain/nervous system?
The paragraph is using explanation to refer to that biochemical scientific understanding of an action. And it's using justification to refer to how our mind's understanding that action, as an action we chose to do based on reasons we considered.
Many psychologists are saying that sometimes there's a justification for an action (i.e. Jason has plenty sufficient reasons to kiss Stella), but that doesn't play any role in the causal explanation.
However, rational actions are when the mental dialogue of why the person is doing the action is actually a crucial part of the causal explanation of the action.
Goal
You got me, sister. When we're doing an Inference problem (MBT or MSS) and we get a stimulus this dense, it's usually very hard to predict an answer, so we just read it a second time, slowly, for good comprehension and then see what the answers are offering us.
With each one, we'll just agnostically ask,