Why is axiom 5, in the list of Euclid’s axioms, considered a 'universal truth'?
(Note that, the question is not about the fifth postulate.)

According to axiom 5, we have 'The whole is greater than a part', which is a universal truth.

Let a line segment PQ = 8cm. Consider a point R in its interior, such that PR = 5cm.

Clearly, PR is a part of the line segment PQ and R lies in its interior.

Hence, PR is smaller than PQ.



Hence, the whole is greater than its part is proved.