I'm recovering a thread I started to follow a few years ago that considered TC's and Comp's treatment of heuristics. My coordinating theme was Speech Act Theory. I argued then that TC departs from Comp's treatment of heuristics at the point were traditional rhetorical techniques fail to help readers adequately learn complex tasks. Such tasks require representations at a level higher than what is possible with traditional rhetorical tropes and techniques; readers/users can see their conceptions described in the documentation.
As with most of my writing, thinking, and teaching, things look so much more narrow and limiting through the lens of experience. However, I do still space for Speech Act as a bridging theory for TC and IDDE. In a recent re-reading of a few Redish essays, I'm again intrigued by the way she invokes the reader/user as an active participant in the writing process. More importantly, her treatment of "reading to do" and "reading to learn" activities places the TCer in the same design/development space as the IDer when creating particular types of information products. Reddish illustrates this common location by having us consider the tutorial as a specific type of information product -- one that requires the user to read "to learn to do."
"... treating reading-to-learn-to-do materials like traditional reading-to-learn materials doesn't work. Tutorial users will not read long prose passages, advanced organizers, or prose summaries... we have to build knowledge through their use of the product, not by giving them pages and pages to read."
This is the point at which I see TC looking toward IDDE. While there are a few TC programs that include exposure to instructional design theory, most practicing TCers "do" ID without much theoretical framing. Consider this comment from Tom Johnson, a highly respected practitioner and TC blogger: "From what I could gather reading Kulman’s blog, the basics of instructional design are fairly intuitive. Create active versus passive learning, give the user control, help the user apply the learning while he or she is learning, select content using the 80/20 rule... Not sure I would need a PhD in instructional design for this, but surely the same could be said of tech comm."
I'm digressing a bit here... I'm still trying to fit activity theory into this space between creating "reading-to-learn" and "learning-to-do" information projects. In a very tangible way, activity theory gives the TCer the means by which to shape text in such a way as move the reader to learn and to do.
More on this to come.