Consistent; logical (8)
I believe the answer is:
coherent
This clue is a double definition.
'consistent' is the first definition.
(I know that consistent can be written as coherent)
'logical' is the second definition.
(I know that logical can be written as coherent)
(Other definitions for coherent that I've seen before include "Able to speak logically" , "Not rambling in speech or reason" , "Clear and logical, not confused" , "Articulate" , "Meaningful" .)