When I Recall Today My Early Youth,

What Mach Calls A Thought Experiment Is Of Course Not An Experiment At All. At Bottom It Is A Grammatical Investigation.

The Mathematician Who Pursues His Studies Without Clear Views Of This Matter, Must Often Have The Uncomfortable Feeling That His Paper And Pencil Surpass Him In Intelligence.

To Us Investigators, The Concept 'soul' Is Irrelevant And A Matter For Laughter. But Matter Is An Abstraction Of Exactly The Same Kind, Just As Good And Just As Bad As It Is. We Know As Much About The Soul As We Do Of Matter.

All This, The Positive And Physical Essence Of Mechanics, Which Makes Its Chief And Highest Interest For A Student Of Nature, Is In Existing Treatises Completely Buried And Concealed Beneath A Mass Of Technical Considerations.

Everyone Is Free To Set Up An Opinion And To Adduce Proofs In Support Of It. Whether, Though, A Scientist Shall Find It Worth His While To Enter Into Serious Investigations Of Opinions So Advanced Is A Question Which His Reason And Instinct Alone Can Decide. If These Things, In The End, Should Turn Out To Be True, I Shall Not Be Ashamed Of Being The Last To Believe Them.