A similar remark might be extended to every other class of phenomena really peculiar; and, had it been attended to, would have prevented many chimerical attempts at demonstrations of the Indemonstrable, and explanations which do not explain.
"A System Of Logic, Ratiocinative And Inductive (Vol. 1 of 2)"
John Stuart Mill
For instance, the whole of Arithmetic and Algebra has been shown to require three indefinable notions and five Indemonstrable propositions.
"Mysticism and Logic and Other Essays"
Bertrand Russell
There are certain ultimate facts beyond which it is impossible to push our speculative inquiries; certain first or fundamental principles of Reason, which are in themselves Indemonstrable, but which constitute the ground or condition of all demonstration; certain intuitive perceptions, which are widely different from rational deductions, but which determine and govern every process of reasoning and every form of belief.
"Modern Atheism under its forms of Pantheism, Materialism, Secularism, Development, and Natural Laws"
James Buchanan