49. There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion, of which it is every moment necessary for us to treat in all our disquisitions.
49. Metafisikan ez dago ideia ilunago edo ez-ziurragorik, gure diskisizioetan noizbait tratatu beharreko ahala, indarra, energia edo beharrezko konexioa baino.