There are two independent ways of developing the second language acquisition process.
a) Acquisition: Is the process by which humans acquire the capacity to perceive, produce and use words to understand and communicate.
b) Learning: Is a conscious process; is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information.
The Natural Order Hypothesis.
Claims that the acquisition of grammar takes place in a predictable order. This order seemed to be independent of the learners' age, L1 background, conditions of exposure. The child second language order was different from the first language order, but different groups of second language acquires showed striking similarities.
The Monitor Hypothesis.
This hypothesis shows how acquisition and learning are two different processes. The ability to produce utterances in a second language comes from the acquired competence. On the other hand, learning serves only as an editor, or monitor. The learned knowledge helps us to make corrections or change the output of the acquired system.
Krashen has stated three conditions to be met to access the learned system. The three conditions for Monitor are:
1. Time. Second language learners need enough time to think consciously about the rules they learned. 2. Focus on form. Besides time, the learner needs to focus not only on what to say but also how to say it, the form.
3. Know the rule. Second language learners should know the rules of the language in order to use them.
Krashen has divided second language learners when using the Monitor process into three types due to their individual differences. These three types are:
a) Monitor overusers.
b) Monitor underusers.
c) Optimal users.
The Input Hypothesis.
Krashen's attempt to explain how the learner acquires a second language. So, the Input hypothesis is only concerned with 'acquisition', not 'learning'.
Conditions:
1) The acquire must understand input that contains i+1. The teacher must provide comprehensible input.
2) According to our traditional assumption we first learn structures, but the input hypothesis claims the opposite, we acquire by "going for meaning" first, and as a result we acquire strucute.
3) According to this hypothesis is simply to provide comprensible input.
The Affective Filter Hypothesis.
This hypothesis, embodies Krashen's view that a number of 'affective variables' play a facilitative role in second language acquisition. These variables include: motivation, self-confidence and anxiety. When the filter is 'up' it impedes language acquisition. On the other hand, positive affect is necessary, but not sufficient on its own, for acquisition to take place.