Rationale / basis / reasons / reasoning

razões, justificativa, fundamentação, motivo/razão subjacente [an underlying reason]: an explanation of controlling principles of opinion, belief, practice, or phenomena; an underlying reason :  basis
The rationale for starting the school day an hour later is that kids will supposedly get an extra hour of sleep.
The rationale underlying legislative decisions to make an appropriation statutory in the first instance vary. Reasons include:..
They told everyone the reasoning behind the decision.
a conclusion based on fallacious reasoning
Humans possess the power of reasoning.