Which term describes illogical and incomprehensible speech?

• A. Derailment
• B. Flight of ideas
• C. Incoherence
• D. Clanging

Answer: (C)

Illogic and lack of understandable structure in speech point to a breakdown in thought form called incoherence. When someone speaks incoherently, the words and sentences don’t connect in a logical way, making the overall communication incomprehensible—like sentences that wander, combine unrelated ideas, or appear as word salad. This is distinct from other disorganized speech patterns: derailment involves thoughts drifting off topic with loose connections but often some intelligible content; flight of ideas features rapid, pressured speech with quick topic shifts that may still be related in meaning; and clanging uses speech tied to sound, rhymes, or rhythm rather than meaning, which disrupts sense in a different way. Incoherence most directly matches the description of speech that cannot be understood due to disorganized thought.