What, if anything, can it possibly mean to deny the existence of the soul--the one and only thing that we have direct experience of?
I can see why someone might deny the existence of a physical universe: we can only experience it as part of the content of consciousness: that is, of the soul.
And I can understand why one might question some aspect of the soul: is it material or immaterial, mortal or immortal. But I don't see how one can question its existence without making use of the very thing they're questioning.
To deny the existence of the soul seems to require some special definition of "soul"--but what?
What is being asked when questions of the existence of the soul are raised?