The Natural Approach
Was developed by Tracy Terrell and Stephen Krashen, starting in 1977. It came to have a wide influence in language teaching in the United States and around the world. it places less emphasis on teacher monologues, direct repetition, and formal questions and answers, and less focus on accurate production of target language sentences.
In the Natural Approach there is an em¬phasis on exposure, or input, rather than practice; optimizing emotional preparedness for learning; a prolonged period of attention to what the language learners hear before they try to produce language; and a will¬ingness to use written and other materials as a source of comprehensible input.
As part of the Natural Approach, students listen to the teacher using the target language communicatively from the very beginning. It has certain similarities with the much earlier Direct Method, with the important exception that students are allowed to use their native language alongside the target language as part of the language learning process. In early stages, students are not corrected during oral production, as the teacher is focusing on meaning rather than form (unless the error is so drastic that it actually hinders meaning).
Communicative activities prevail throughout a language course employing the Natural Approach, focusing on a wide range of activities including games, role-plays, dialogs, group work and discussions. There are three generic stages identified in the approach: (1) Preproduction - developing listening skills; (2) Early Production - students struggle with the language and make many errors which are corrected based on content and not structure; (3) Extending Production - promoting fluency through a variety of more challenging activities.
Krashen's theories and the Natural approach have received plenty of criticism, particularly orientated around the recommendation of a silent period that is terminated when students feel ready to emerge into oral production, and the idea of comprehensible input. Critics point out that students will "emerge" at different times (or perhaps not at all!) and it is hard to determine which forms of language input will be "comprehensible" to the students. These factors can create a classroom that is essentially very difficult to manage unless the teacher is highly skilled. Still, this was the first attempt at creating an expansive and overall "approach" rather than a specific "method", and the Natural Approach led naturally into the generally accepted norm for effective language teaching

Theory of language
The Communicative view of language is the view behind the Natural Approach. Particular emphasis is laid on language as a set of messages that can be understood
Theory of learning

The Natural Approach is based on the following tenets:
 Language acquisition (an unconscious process developed through using language meaningfully) is different from language learning (consciously learning or discovering rules about a language) and language acquisition is the only way competence in a second language occurs. (The acquisition/learning hypothesis)
 Conscious learning operates only as a monitor or editor that checks or repairs the output of what has been acquired. (The monitor hypothesis)

 Grammatical structures are acquired in a predictable order and it does little good to try to learn them in another order.(The natural order hypothesis).

 People acquire language best from messages that are just slightly beyond their current competence. (The input hypothesis)

 The learner's emotional state can act as a filter that impedes or blocks input necessary to acquisition. (The affective filter hypothesis)

These five hypotheses have obvious implications for language teaching.

1. THE ACQUISITION-LEARNING DISCTINCTION
Adults have two different ways to develop competence in a language: language acquisition and language learning.
Language acquisition is a subconscious process not unlike the way a child learns language. Language acquirers are not consciously aware of the grammatical rules of the language, but rather develop a "feel" for correctness. "In non-technical language, acquisition is 'picking-up' a language."
Language learning, on the other hand, refers to the "conscious knowledge of a second language, knowing the rules, being aware of them, and being able to talk about them." Thus language learning can be compared to learning about a language.
The acquisition-learning distinction hypothesis claims that adults do not lose the ability to acquire languages the way that children do. Just as research shows that error correction has little effect on children learning a first language, so too error correction has little affect on language acquisition.

2. THE NATURAL ORDER HYPOTHESIS
The natural order hypothesis states that "the acquisition of grammatical structures proceeds in a predictable order." For a given language, some grammatical structures tend to be acquired early, others late, regardless of the first language of a speaker. However, as will be discussed later on in the book, this does not mean that grammar should be taught in this natural order of acquisition.

3. THE MONITOR HYPOTHESIS
The language that one has subconsciously acquired "initiates our utterances in a second language and is responsible for our fluency," whereas the language that we have consciously learned acts as an editor in situations where the learner has enough time to edit, is focused on form, and knows the rule, such as on a grammar test in a language classroom or when carefully writing a composition. This conscious editor is called the Monitor.
Different individuals use their monitors in different ways, with different degrees of success. Monitor Over-users try to always use their Monitor, and end up "so concerned with correctness that they cannot speak with any real fluency." Monitor Under-users either have not consciously learned or choose to not use their conscious knowledge of the language. Although error correction by others has little influence on them, they can often correct themselves based on a "feel" for correctness.
Teachers should aim to produce Optimal Monitor users, who "use the Monitor when it is appropriate and when it does not interfere with communication." They do not use their conscious knowledge of grammar in normal conversation, but will use it in writing and planned speech. "Optimal Monitor users can therefore use their learned competence as a supplement to their acquired competence."

4. THE INPUT HYPOTHESIS
The input hypothesis answers the question of how a language acquirer develops competency over time. It states that a language acquirer who is at "level i" must receive comprehensible input that is at "level i+1." "We acquire, in other words, only when we understand language that contains structure that is 'a little beyond' where we are now." This understanding is possible due to using the context of the language we are hearing or reading and our knowledge of the world.
However, instead of aiming to receive input that is exactly at our level, or instead of having a teacher aim to teach us grammatical structure that is at our level, we should instead just focus on communication that is understandable. If we do this, and if we get enough of that kind of input, then we will in effect be receiving and thus acquiring out i+1. "Production ability emerges. It is not taught directly."
Evidences for the input hypothesis can be found in the effectiveness of caretaker speech from an adult to a child, of teacher-talk from a teacher to a language student, and of foreigner-talk from a sympathetic conversation partner to a language learner/acquirer.
One result of this hypothesis is that language students should be given a initial "silent period" where they are building up acquired competence in a language before they begin to produce it.
Whenever language acquirers try to produce language beyond what they have acquired, they tend to use the rules they have already acquired from their first language, thus allowing them to communicate but not really progress in the second language.

5. THE AFFECTIVE FILTER HYPOTHESIS
Motivation, self-confidence, and anxiety all affect language acquisition, in effect raising or lowering the "stickiness" or "penetration" of any comprehensible input that is received.
These five hypotheses of second language acquisition can be summarized: "1. Acquisition is more important than learning. 2. In order to acquire, two conditions are necessary. The first is comprehensible (or even better, comprehended) input containing, structures a bit beyond the acquirer’s current level, and second, a low or weak affective filter to allow the input 'in'."

Objectives
it is designed to help beginner become intermediates
It is designed to depend on learner needs.
The syllabus
The syllabus for the Natural Approach is a communicative syllabus.
Types of learning techniques and activities
 Comprehensible input is presented in the target language, using techniques such as TPR, mime and gesture.
 Group techniques are similar to Communicative Language Teaching.
 Learners start to talk when they are ready.