It is a matter of some importance and also a matter which falls properly within the province of philosophy, to discuss the question what sort of proof, if any, can be given of ‘the existence of things outside of us’. And to discuss this question was my object when I began to write the present lecture. But I may say at once that, as you will find, I have only, at most, succeeded in saying a very small part of what ought to be said about it.
People often talk as if nothing were easier than for two naked minds to “meet” or become aware of each other. But I see no possibility of their doing so except in a common medium which forms their “external world” or environment.