Reason I will get into record by contralto (5)
I believe the answer is:
logic
'reason' is the definition.
(logic is using reason)
'i will get into record by contralto' is the wordplay.
'will get into' indicates putting letters inside.
'record' becomes 'log' (log is a kind of record).
'by' means one lot of letters go next to another.
'contralto' becomes 'c' (musical abbreviation).
'log'+'c'='logc'
'i' going inside 'logc' is 'LOGIC'.
(Other definitions for logic that I've seen before include "good sense" , "Dialectics" , "this makes sense" , "The science of reasoning from cause to effect" , "Science of correct reasoning" .)