Some key concepts in syntax:

• Constituency: groups of words which function together as a unit (movement, substitution: "Jill ate the peach", "Jill ate it", "The peach, Jill ate")
• Recursion: a constituent may contain another constituent of the same type ("the woman's mother's friend...", "Jill said that Jack hinted that Bill wanted Max to tell Bruce to eat the bagel")
• Linear order: order of sister constituents ("Subject before verb phrase")
• Subcategorization, selection: certain items (esp. verbs) have "slots" which require certain kinds of fillers ("Jill put the book on the table", "*Jill put the book", *"Jill put" etc.)
• Dependency: constituents have heads (required items) and dependents ("modifiers", often optional). Every noun phrase must have a noun, so the noun is the head of the noun phrase.

Context-free grammars (usually called "phrase structure grammars" by linguists): specify a tree structure by means of "rewrite rules."

Download the Excel sentence generator here to see an example.

How would you need to modify this kind of grammar to get better sentences?