> You are using language invented elsewhere while claiming you can't be sure of its reality.
Your senses are the only thing on which this statement rests. Your don't know anything like "language", "invented" etc. All you know is what your mind and your senses tell you.
And, yes, engaging with you on this topic, and my argument, is also included in what I refer to as my perception. I have no way to prove that you are even conscious, or that anything like language or invention actually are real, whatever real means.
So it's through the senses that one attains mathematical knowledge?