Related Clues:

• "Of this ___ certain"
• Descartes's 'sum'
• "No kidding?"
• "Really?"
• 15-Down's Sam- --
• ''__ the Walrus''
• Thinker's conclusion
• Answer to 'Are you or are you not?'
• "For sure!"
• "No lie!"
• ''How sweet ___!''
• Affirmative response
• Decartes' conclusion
• "__ the Walrus"
• 'Verily'