[arcsin]

Yes and no. I’m someone who took krashen to heart and learned almost exclusively though reading. What I’ve found is that it’s possible to understand everything as long as it’s written or spoken very slowly and clearly but this is a different thing to understanding the spoken language at a normal speaking pace. It’s too fast and at that speed often sound alone is not clear enough to distinguish words. For example if you took a recording and cropped the audio just before and after each word I think there will be many words you will not recognize out of context.

I think the way that we are able to process speech at that speed is that we essentially guess what words are coming next, which is really only possible if you’re able to construct the sentence yourself. If you stop a sentence at a random point a native speaker will be able to predict the kind of words that will come next, if not the exact words. Another bit of evidence for this theory is that if someone says something very unexpected and out of context we often won’t understand what they’ve said.

Now it’s possible that you could achieve this ability only through input and not through production but I believe that it will be much less efficient.