I don't think it's a tautology, just getting too hand-wavy on an important point. What does it mean to really use a programming language? I take it to mean tha

I don't think it's a tautology, just getting too hand-wavy on an important point. What does it mean to really use a programming language? I take it to mean that your task aligns with the strengths of the language. I can use the butt of a screwdriver to drive in a nail, but hammers certainly are better at the task. Programming languages are similar, but defining the strengths of the languages and the needs of your task are monstrously more complex. One strength, and weakness, of Lisp is its malleability. The language itself can be turned into almost anything you want or need. If your purpose is to demonstrate possibility, few tools are better. At this point you can really use Lisp, because at this point you are free to exercise the strengths that only Lisp has. Once that possibility is known, though, this strength becomes a form of weakness. The project should now move with purpose, methodically exploring the problem space. You draw attention, hopefully money, and with it more team members. What was a single vision wrought in code now must be the coordinated effort of a large group. You can no longer really use Lisp because the group is too large and sharing the knowledge of a newly built language feature takes more time than the feature saves. So, you stop really using Lisp and just use it, carefully selecting the subset of tools that allow people to work together. Or, you rewrite, in some language whose strengths are more in line with the needs of your now larger project. Then you are really using that language. I don't see tautology or contradiction here, only shifting requirements that we fail to acknowledge.