The meaning of things being communicated is more important for second language acquisition than their form. There is a general agreement among researchers that learners must be engaged in decoding and encoding messages in the second language for the conditions to be right for second language learning. Learners must also be engaged in creating pragmatic meaning in order to develop fluency.
Some sort of focus on form does appear to be necessary for second language acquisition, however. Some advanced language structures may not be fully acquired without the opportunity for repeated practice. Schmidt's noticing hypothesis states that conscious attention to specific language forms is necessary for a learner's interlanguage to develop. This attention does not have to be in the form of conscious grammar rules, however; the attention is on how each specific form affects the meaning of what is being said.
Developing subconscious knowledge of the second language is more important than developing conscious knowledge. While conscious language knowledge is important for many aspects of second language acquisition, developing subconscious knowledge is vital for fluency. The knowledge that people use when they are speaking a language is mostly subconscious. It appears that learners can use conscious knowledge in speech if they have time and they are focused on form, but if these conditions are not met then they will fall back on subconscious knowledge. However, if learners have time to plan their speech, grammatical accuracy can improve.
It is not certain exactly how subconscious language knowledge is developed in the mind. According to skill-building theory, subconscious language knowledge is gained by practicing language until it becomes automatic. However, according to emergentist theories subconscious knowledge develops naturally from input and communication. The nature of the interface between conscious and subconscious language knowledge in the brain is also not clear; that is, it is not clear how conscious knowledge can develop into subconscious knowledge. It appears that conscious knowledge and subconscious knowledge are not completely separate, and practice at various aspects of language can lead to language knowledge becoming subconscious. However, studies have found that the two types of knowledge are stored differently in the brain, and this has led to the idea that conscious knowledge merely primes language acquisition processes rather than being directly involved. Both of these issues are still under debate.
The way learners process sentences in their second language is also important for language acquisition. According to MacWhinney's competition model, learners can only concentrate on so many things at a time, and so they must filter out some aspects of language when they listen to a second language. Learning a language is seen as finding the right weighting for each of the different factors that learners can process.
Similarly, according to processability theory, the sequence of acquisition can be explained by learners getting better at processing sentences in the second language. As learners increase their mental capacity to process sentences, mental resources are freed up. Learners can use these newly freed-up resources to concentrate on more advanced features of the input they receive. One such feature is the movement of words. For example, in English, questions are formed by moving the auxiliary verb or the question word to the start of the sentence (John is nice becomes Is John nice?) This kind of movement is too brain-intensive for beginners to process; learners must automatize their processing of static language structures before they can process movement