Related Clues:

• Determining factor
• Ninny's lack
• Underlying cause
• Use one's noodle
• Incentive
• The underlying cause
• "Romeo and Juliet" word that actually means "why"
• Motive for action
• What Kant critiqued
• Rhyme alternative
• Be logical
• Lucidity
• Make a deduction
• Use logic
• The right exercise of the mind