In this chapter we begin to work through basic concepts of logic in more detail. The focus is on validity and on what negation is. We introduce a technique that is used throughout the book for revealing the structure of natural language arguments, and we continue the discussion of the liar.

Formal topics:

• Argument validity
• Negation

Informal topics:

• How to diagram an argument.

Supplementary topics:

• The strengthened liar paradox
• The LSAT
• Puzzles