That's quite an interesting view. Thanks for sharing it!
As it happens, I'm in significant disagreement with you. For one thing, I do not understand why your the best case must be
the best case. I would think it possible for someone using a new definition of a word with a well established meaning to point out that he or she is using the word in a new way and then define his or her usage of the word. If they did that, then wouldn't the best case be that others understood them -- rather than the best case being miscommunication and confusion?
Can it be acceptable to use a new definition for a concept that already has a well-accepted definition? I don't see why not. Doing so violates no laws of humanity or nature. So long as the new definition is made explicit what is the harm?
It seems to be advantageous at times to redefine words with well-accepted definitions for various purposes -- very much including to reflect new knowledge or accommodate new concepts.
For instance, the word "paradigm" once had a well-accepted definition of referring to a form or template for something. Then along came Thomas Kuhn in the early 60s. His new usage of the word proved to be so popular and useful to so many people that nowadays, a few decades later, most of us use "paradigm" to more or less mean what Kuhn meant by it. Do you consider Kuhn's redefining of paradigm "acceptable"? Do you think it at best led to "miscommunication and confusion"?
Again, based on what little I know of the sciences, it seems to me that words with well-accepted meanings are being redefined all the time. How many alterations in meaning has the word "intelligence" gone through in the field of psychology for any of several reasons?
Beyond that, very few people in my experience perfectly adhere to the dictionary definition of every word they use despite that dictionaries usually report the most common and well-accepted usages of words. And yes, that often enough leads to miscommunication and confusion, but it also sometimes leads to better communication of various concepts when a new usage someone has coined takes off and becomes popular.
For instance, there seems to be a relatively recently coined meaning for the word "Pablo". Pablo used to refer only to the proper name of some persons. But a few years ago, I began now and then hearing it used in reference to a
kind of person -- near as I can figure it out, a "Pablo" is a very smart man who doesn't act like he's smart. If so, it seems like a pretty useful expansion on the language to me because I don't know of any other word that conveys exactly the same meaning as the new meaning of "Pablo". Pablo is not a perfect example of what I'm getting at, but I hope you can get the idea. Redefining the meanings of well-accepted words can sometimes enrich the language and even lead to providing an easier way to communicate an old or new concept.
Using old words in new ways can certainly create problems, I will grant you that. But those problems often enough seem to me outweighed by the legitimate advantages that can sometimes be had by doing it.
That would be an excellent point if only it were relevant. If you will re-read the first argument, you'll notice it is not about whether god exists or not. So to say that it's "shifting the goalposts" for whether god exists or not strikes me as a misunderstanding.
It seems to me that "Lincoln's" point can be rephrased as "defining a word in a way that conflates two distinct things does not make the two things the same thing in reality". I agree. But here's where I think we disagree:
In essence, I am arguing that to define a term as X does not necessarily mean you are conflating X with Y simply because Y is the prior or more common meaning of the term. To redefine "house cat" as "an exceptionally sexy housewife" does not necessarily mean you are conflating "an exceptionally sexy housewife" with "a small domestic feline" simply because "a small domestic feline" is the prior or more common meaning of the term "house cat".
Yet -- if I understand you correctly -- you are in essence arguing the converse of my position.
Have I understood you correctly?
At any rate, thank you for making such interesting points. It's fun discussing this with you. You always get me thinking.