Lear experiences lucidity, 'reason', and exhibits his most profound moments when he is mad. This is the central irony in Lear and reflects both the contradiction, which is a convention of Classical tragedy and the essential uncertainty of the human condition, which the play ultimately expresses. 

-  'Reason' in madness - as the idea that the suffering of both Lear and his foil Gloucester is not futilie - relate to the tragic vision. 

- Either: suffering as productive: Lear as affirmative of the Christianity 

- Or: there is essentially no 'reason' in the suffering - overwhelming impression of waste.