Is there some precise universal criterion of truth which will be applicable at all times and under all circumstances, in short, something unchanging and therefore supreme? For scientists know that the great principles which formed landmarks in the history of science were really successive stages on the route towards the precise truth. Science changes, its doctrines change, and its earlier approximations are replaced from time to time by more accurate points. We cannot hope to find an ultimate truth nowadays, when science itself is so rapidly on the march. There remains, however, one unfailing all-embracing fact which will forever remain true and which cannot possibly change. Indeed, every advance in experiment and theory made by enterprising scientists will only help to verify this grand discovery. What is it? It is that the whole world which every department of science is busily engaged in examining is nothing but an idea in the human mind. Physics, chemistry, geology, astronomy, biology, and all the other sciences without a single exception are concerned solely with what is ultimately a thought or series of thoughts passing through human consciousness. Here, therefore, we possess a universal law which embraces the entire field in which science is operating. This is an ultimate truth which will stand immortal, when every other hypothesis formulated by science has perished through advancing knowledge.
-- Notebooks Category 21: Mentalism > Chapter 4 : The Challenge of Mentalism > # 170
-- Perspectives > Chapter 21: Mentalism > # 49
