Acquisition must be sustained by input

In 1980, Stephen Krashen designed a theory call the input theory. Such theory argues that all of the learners who want to speak a new language must follow a proper process. Krashen noticed many people failed on language learning due to misconceptions themselves had imposed. For instance, many people considered that the exercises for learners must be whose level were the highest. But it only fostered frustrated learners.  Krashen thought about a real and effective solution and wrote on the importance of input.

But What is input?

In simple terms, it can be defined like the entrance of information that a person has from another language. It means that, all of the stimuli and exposure learner receives can be called input. For instance, Music in another language, conversations with people who know the target language, movies, readings. Etc.

However, according to Krashen, input must be comprehensible. It is not good for a learner to be exposed to different kinds of input, which are not functional and comprehensible.  As long as, learner can understand the kind of exposure, they will have important results and will be able to transform those different resources and information into language evidences. (Orally, writing, listening or speaking)

It will also motivate the production of language. Learner will have the need to share in a tangible way what is being learning by him/her. That is what Krashen called Output.

To Conclude 

Learner must be surrounded by proper contexts where can  acquire overtime. That is directly related to the production of language or Output in academic terms. The more you acquire the more you produce.