> I used logically sound. Do you personally think logically sound and sound argument mean the same thing?
Well, the real point is that it is not clear what you mean here, and consequently what you are writing is likely to cause confusion and misunderstanding. In particular, as I pointed out in an earlier post, you were inconsistent in your own usage, sometimes using 'sound' correctly, and sometimes incorrectly.
You also seem to think that because, in a series of follow-up posts, you can explain what you meant, then it follows that there was nothing wrong with your original post - but if no-one had replied to it, you would not have corrected it on your own, and it would have remained there, sowing confusion among those who did not know it was wrong (and, of course, being useless to those who do know it is wrong.)
The size of the responses to your original post is a clear testament to the way private usage inhibits understanding and spreads confusion (though there would be considerably less if you had simply acknowledged your mistake immediately, and henceforward used 'sound' in its conventional sense.)
> Private languages and the acknowledgement of them is not useless.
I said that they are useless for communication (of course, they can be useful to the extent that they are not entirely private, but that caveat actually bolsters my point.)
>It's a basis for being able to clarify things...
Quite the opposite, as shown here: it's most often a basis for confusion and misunderstanding - and how could it not be? You have to achieve a shared meaning before there can be clarity and mutual understanding.