Krashen's Five Hypotheses on Second Language Acquisition

This hypothesis states that adults have two distinct ways of developing competence in a second language: acquisition (a subconscious process similar to how children learn their first language) and learning (conscious knowledge of language rules, like grammar). Acquisition leads to a 'feel for correctness,' while learning involves knowing and being able to talk about the rules. This hypothesis suggests adults can still acquire languages like children and that error correction has little effect on acquisition.

This hypothesis posits that language rules are acquired in a predictable order, regardless of how they are taught. This order is consistent for both first and second language acquisition, although the specific order can differ between the two. For example, English learners often acquire 'yes/no' questions before 'wh-questions'. Research by Brown, Dulay, and Burt supports this, showing consistent morpheme acquisition orders in both first and second language learners.

This hypothesis suggests that acquisition initiates utterances and is responsible for fluency, while learning acts only as a 'monitor' or editor for output. The monitor allows for self-correction before or after speaking when there is sufficient time, a focus on form (correctness), and knowledge of the rule. Krashen categorizes monitor users into over-users (hesitant, overly concerned with correctness), under-users (rely solely on acquired system, uninfluenced by error correction), and optimal users (use the monitor appropriately without hindering communication).

This hypothesis states that second language acquisition occurs through exposure to 'comprehensible input' that is slightly beyond the acquirer's current level of competence (i+1). This is analogous to 'caretaker speech' used with children learning their first language. Krashen identifies various forms of comprehensible input, including 'teacher talk' (classroom language), 'foreigner talk' (simplified speech by native speakers), and 'interlanguage talk' (speech among second language acquirers).

This hypothesis explains why acquirers may receive comprehensible input but still not reach native-like proficiency. It proposes an 'affective filter' that acts as a mental block, preventing input from being used for acquisition. The filter's strength is influenced by emotional factors like motivation (high motivation leads to better acquisition), self-confidence (good self-image improves acquisition), and anxiety (low anxiety is conducive to acquisition). Optimal learning environments are those that lower this filter, promoting a low-anxiety atmosphere.