And both of these are dependent upon the acceptance of the...

And both of these are dependent upon the acceptance of the principle of causality, before setting out to experiment, for if an experimenter does not believe in the principle of causality, and he seeks to establish this by means of an experiment, he will not be able to ascertain the real existence of things experimented, for it is in the light of this principle that we ascertain the existence of a cause (an external thing) by means of the existence of its effect (a perceptual phenomenon), as was explained in Lesson Twenty-Three.

Furthermore, unless it is established with the help of the laws of causation that the causes of various changing perceptual phenomena indicating different dimensions and shapes correspond to material things, one will not be able to know definitely and certainly the attributes and characteristics of the objects of experience, so that one may be able to make judgments about the results of experiences related to them.

Moreover, the utmost that can be ascertained through sense experience are merely simultaneity or the regular succession of two phenomena in the realm of experience. However, we know that simultaneity or the succession of phenomena are more general than causality, and by means of them the causal relation cannot be established.

Finally, the problem remains that no matter how many times a sense experience is repeated, it cannot refute the possibility of an uncaused effect; that is, there will always remain the possibility that in the case of something not yet experienced the effect will occur without the cause, or while the cause exists, its effect does not occur, i.e., sense experience is insufficient to establish the universal and exigent relation between two phenomena, let alone establish the universal laws of causality regarding all causes and effects.

Hence, someone like Hume, who considers causality to amount to the simultaneity or succession of two phenomena will be unable to escape from such doubts and misgivings, and for this reason this sort of philosophical problem has been declared to be unsolvable. Likewise, those who have inclinations toward positivism and who restrict themselves to the input of the senses cannot establish any universal and definite laws in any of the sciences.

Therefore, it is necessary to provide further explanation of the purport of the principle of causality, its value and its validity.