Reason out
Definition 1 of 1
Pro Tip 1/3Logical Process
Use 'reason out' when describing the systematic process of thinking to solve a problem or make a decision. 
She managed to reason out the best approach to handle the customer complaint.
Pro Tip 2/3Problem Solving
'Reason out' often implies there's an issue or complex matter that needs a logical explanation or solution. 
The detective tried to reason out the sequence of events leading up to the crime.
Pro Tip 3/3Not Guesswork
The phrase is not used for making guesses, but for thinking that is supported by facts and evidence. 
To win the debate, we need to reason out our arguments based on solid data.