And in spite of the talk about discarded standpoints, they possess in a measure the per certain relative validity.
(from History of Modern Philosophy by Richard Falckenberg)
According to the passage, why do systems of philosophy retain a certain relative validity?
O 1. Aspects of the systems are difficult to disprove.
2. Important tenets of the systems have been proven to be infallible.
3. The systems are based on rigorously tested proofs and theorems.
4. The systems draw on both the arts and natural science.