Grammatik is WordPerfect's grammar checker. A grammar checker proofs documents for correct grammar, style, punctuation, and word use, and thus catches many errors that get by most spell checkers. Interestingly, Spell Checker is integrated into Grammatik, so you only need to run Grammatik to run both.
Grammatik uses grammatical rules when checking a document for problems. Many good writers, however, often bend these rules to make a point. You shouldn't feel compelled to fix every problem or accept every suggested solution if it changes the meaning of your words.
To start Grammatik and check your document
Choose Tools, Grammatik (Alt+Shift+F1) or if you already have the Writing Tools dialog box open, just click ...