Thanks, Robert. I appreciate your comments and the link to your article. In writing about the associative aspect of idea networks, I wasn't describing a detailed mechanism. You may well be right about some of the details, and I agree that grammar and predication are involved in multi-word expressions.

But it only requires two words to invoke associations between concepts -- "invisible locomotive" for example, or "elephant squirrel". What those bring to mind in your brain will not necessarily be the same as what they bring to mind in mine. Is your invisible locomotive steam powered or diesel? If it is steam powered, is the water vapor invisible, too, or just the locomotive?

Is your elephant squirrel the size of an elephant or the size of a squirrel? What color is it and what might it eat? It probably has a trunk like an elephant, but does it have a bushy tail like a squirrel?

And now that I have brought those ideas to your mind, your brain may make, or may already have made, permanent connections between them that form part of your long-term memory.