#tprs

Of course! Comprehensible input is input (listening or reading) that is 90% + comprehensible to you, or i + 1. That is to say just beyond your own abilities. It allows you to use what you know to contextualize new words and structures plus get in more repetitions of familiar structures.

On average, it takes 50-70 repetitions of a structure to remember and use quickly and correctly, but 150-500 is much better for long term retention as well as understanding nuance.

The idea is that you can’t actually force yourself to learn the “rules” of language in order to produce it, especially if you want to produce it fluidly on the spot. Instead, you acquire the rules and structures through comprehensible input. Other factors like openness to understanding and a low affective filter (comfort with participating in communication) are also very important.

Associated is the idea of the silent period, where very little output is happening, but a large amount of input is being processed. Much like first language acquisition. Forcing output based on some rule repetitions doesn’t seem to have any appreciable impact on actual language acquisition. Reading, however, does. Like a lot. Even super language learners like Daniel Tammet (Brainman) use an incredible memory (conscious learning) and acquisition strategies (subconscious) like reading and listening to the radio. 

Ultimately, you have to be motivated to use a language if you want to produce output, but the quality of that output depends greatly on the amount on comprehensible input you are receiving.

Some research, if you’re interested:

Krashen - so many articles here (free)

Batterink & Neville - The Human Brain Processes Syntax in the Absence of Conscious Awareness

VanPatten - The Two Faces of SLA: Mental Representation and Skill

Ellis - Principles of Instructed Language Learning