Krashen claims that language acquisition occurs through understanding messages or, in other words, through receiving “comprehensible input”. That is, in Krashen’s view, perceptive language behaviours such as listening or reading play the major role in the learning process, while everything else, including the development of speaking skills or the knowledge of grammar rules, will follow automatically as long as a sufficient amount and type of input is provided. Therefore, a student cannot be expected to produce “i+1” output without learning first about the “+1” element, that is, without receiving some sort of “i+1” input.