By part of speech

• By entity (noun)
  • who: By protagonist (human noun; see also Person, human, individual)
  • what: Thing
  • when: Event
  • where: By location
  • how: How-to/Process
  • why: Concept/By emotion
• By relationship - Relationship between two subjects (e.g., 'Abdu'l-Bahá and Leo Tolstoy) (conjunction or preposition)
• By action (verbs)
• By description (adjectives or adverbs)
• By expression of emotion (interjection)