Listening is fundamental to second language learning; indeed, it is probably the most important skill underlying the development of a second language.

One of the most influential recent models of second language acquisition has been Steven Krashen's (1985) Input Model. This claims that second language acquisition is driven by learners' attempts to make sense of language which is addressed to them. Once learners start to understand target language 'input', Krashen claims that they will automatically pick up the grammar. All that is necessary is meaningful or comprehensible input: there is no need to learn grammar rules explicitly.

But how do learners make input comprehensible if they don't already have a knowledge of the grammar and vocabulary? Krashen argues that learners use their knowledge of the world to guess at the meaning; furthermore, he claims, speakers automatically simplify their language in order to get their message across to learners.

Few researchers would disagree that extensive exposure to meaningful target language is essential in second language development. Written texts can of course provide comprehensible input, but if a learner is going to speak the target language, then spoken input is essential. Many teachers and researchers have nevertheless challenged Krashen's assumption that 'all you have to do is understand, and the linguistic system will take care of itself'. While comprehensible input may be essential, it may not be sufficient to ensure second language development to high levels of accuracy and complexity.

Van Patten (1989), Schmidt (1990) and Skehan (1998) have all argued that when adults try to understand L2 input, they focus on the content of what is being said, noticing vocabulary items. They may pay some attention to obvious grammatical features such as word order, but many grammatical features such as determiners and word endings are often not noticed, simply because the listener can usually work out the meaning without them.

It seems unlikely that the average adult learner will be able to pay attention to both meaning and form in the target language at the same time. The above authors have claimed that learners' attention needs to be drawn to grammatical features of input after it has been comprehended. In other words, it is not enough to learn to listen (ie just make sense of the target language input); learners also need to listen in order to learn (ie pay attention to the linguistic features of the text in order to retain them). 'Just understanding' is not enough...