An interesting thing about words is that we must always define them in terms of other words, and the same with those words, and so on. So we must either (a) come back to the term with which we started or (b) have an infinitely long chain of words meaning other words. In either event, simply citing the definition of every word does not bring the parties involved to a similar understanding. In mathematics and logic, this problem is avoided using primitive terms, which are terms everyone is expected to have the same understanding of almost innately. In geometry, point, line, and plane are some primitive terms. I don't know what our primitive terms would be in this conversation, but we could always just keep going back until we agree on something.

I would say that is probably a valid distinction. Though, I do have a hard time critical examining something that is entirely immaterial because I lack any faith that it exists. The soul doesn't exist in any physical sense, so what can we possibly say about it objectively?