Input is one of the most important elements in the process of second language acquisition (SLA). As Gass (1997) points out, second language learning simply cannot take place without input of some sort. Since then, specific issues have been actively debated in SLA on the nature of input and input processing, such as the amount of input that is necessary for language acquisition, various attributes of input and how they may facilitate or hinder acquisition, and instructional method that may enhance input. In this paper, four hypotheses and paradigms of input processing have been described. It is delineated that although the three paradigms of triggering, input hypothesis, and interaction hypothesis have been widely used and accepted, they lack the ability to account for the dynamic nature of language. Affordance, on the other hand, can account for such a nature of language.
Therefore, affordance replaces fixed-eye vision by mobile-eye vision; an active learner establishes relationships with and within the environment. The learner can directly perceive and act on the ambient language without having to route everything through a pre-existing mental apparatus of schemata and representation, while this is not true in the fixed-code theory. In the fixed-eye theory of communication it is assumed that ready-made messages are coded at one end, transmitted,
and then decoded in identical form at the other end. We need in its place a constructivist theory of message construction and interpretation.