Nothing is either pure or impure. all depend upon your perception and the relative frame in which the proposition is being evaluated.
Similarly state of inertia or motion are once again relative terms. Nothing is absolute.
Things proved correct may be disproved in another frame or even that very frame taking only a different path to examine that. All depend on the way of your examination. Further more all depend on purity of your tools, accuracy of your methodology and the way the proposition is examined. Time invested in the examination often changes the result. The experience of the examiner , the prejudices of evaluator and individual mindset,environment and other parameters. None of them can be absolute, all time proved correct hence all declaration howsoever authentic they appear  are open to check, challenge, scrutiny and re-examination and we must not feel disappointed if we are challenged sometimes