Krashen's Monitor Model proposes five main hypotheses:
1. The Acquisition-Learning Hypothesis distinguishes between subconscious acquisition and conscious learning of a language.
2. The Natural Order Hypothesis states that grammar structures are acquired in a predictable order.
3. The Monitor Hypothesis describes editing abilities used on language production.
4. The Input Hypothesis claims language is acquired through comprehensible input above one's current level.
5. The Affective Filter Hypothesis involves socio-emotional variables that affect language acquisition.