Stephen Krashen himself has joked in a self-deprecating way that he came up with the vague concept of “i+1” to achieve fame as people argue its meaning indefinitely. Before contacting him, I wasn’t exactly sure how seriously we should take the man! Thankfully, Stephen clarified that for me real quick. Regardless of the joke being aimed at those using academic jibberish, the concept of “i+1” is demystified in the following Krashen-approved commentary…
Many (most?) people referring to “i+1” incorrectly state that “i” is what a learner understands, and “+1” is the next bit of language a learner doesn’t understand. This is not at all what Krashen meant. I’ll admit that I absorbed what those people had been saying over the years, even joking with Latin teachers about how ancient unadapted Latin can feel like “i+10” (except for Tacitus, which feels like “i+100,” right, Johns?). Anyway, I have no problem admitting being totally wrong on that. It just took some time reading the primary source, and cross-referencing findings and ideas with other research. The result? Well…
If a learner doesn’t understand the input, it doesn’t even qualify as “i+1” yet.
The learner must understand language that contains structure just beyond the level of competence. This doesn’t mean that the language should be difficult to understand at all! This also doesn’t mean that learners should only be receiving that kind of input (i.e. input that contains structure just beyond the level of competence). So, an entire class with no new language that’s completely understandable is fine (e.g. instead of 3 new phrases every class, like clockwork, in an attempt to cover a department’s thematically themed vocab and grammar-based curriculum, etc.). Support for this can be seen in research done on Extensive Reading, of which a core principle, at least according to Jeon & Day (2015), is “books are easy.” If books are easy, learners are unlikely to find much “i+1,” but that’s not even an issue according to Krashen’s hypothesis; learners shouldn’t only be receiving that kind of input, because it will be provided automatically over time. The pedagogical implications are that it would be easy for teachers to adopt a content-area mindset of “challenging students” by giving them something hard to read. The problem with this mindset, however, is that none of our research suggests it’s a good idea to do so!
So, CI is input that’s understood, and its relation to acquisition is “i+1.” Those are not the same thing, and we should avoid using the concept to justify giving learners reading that’s above an appropriate level.
Here are Krashen’s precise words on that:
We may thus state parts (1) and (2) of the input hypothesis as follows:
(1) The input hypothesis relates to acquisition, not learning.
(2) We acquire by understanding language that contains structure a bit beyond our current level of competence (i + 1). This is done with the help of context or extra-linguistic information.
A third part of the input hypothesis says that input must contain i + 1 to be useful for language acquisition, but it need not contain only i + 1. It says that if the acquirer understands the input, and there is enough of it, i + 1 will automatically be provided. In other words, if communication is successful, i + 1 is provided. As we will discuss later, this implies that the best input should not even attempt to deliberately aim at i + 1.