[see also: explain, justify, ground] This argument is invalid for several reasons.
It is for this reason that his argument is incorrect.
The definition is stated in terms of local martingales, rather than martingales, for the technical reason that the former are easier to characterize in applications.
This is the reason for calling f the derivative of g.
The reason this is significant is that......
The reason why...... is that......
[see also: argue, proceed] To see this, we reason as follows.
The simplest way is to reason by induction on n.