Chapter 5 addresses well-formedness and introduces alternative logical notation. It continues the discussion of translating English into sentential, and introduces students to supplying suppressed premises or conclusions in natural language arguments. The discussion of the distinction between local and global logical properties encourages students to distinguish between necessary and contingent features of sentences and the relations between them. The supplementary sections show how to apply Polish notation in computer engineering, how considerations of well-formedness in logic apply to natural languages, and introduce the concept of infinity.

Formal topics:

• Well-formed formulas
• Formalization in Sentential
• Polish notation

Informal topics:

• Determining when statements are missing from arguments

Supplementary topics:

• Quine's Paradox
• Hilbert's hotel
• Puzzles