To convince us that all the laws of nature, and all the operations of bodies without exception, are known only by experience, the following reflections may perhaps suffice. Were any object presented to us, and were we required to pronounce concerning the effect which will result from it, without consulting past observation, after what manner, I beseech you, must the mind proceed in this operation? It must invent or imagine some event, which it ascribes to the object as its effect; and it is plain that this invention must be entirely arbitrary. The mind can never possibly find the effect in the supposed cause by the most accurate scrutiny and examination. For the effect is totally different from the cause, and, consequently, can never be discovered in it. A stone or piece of metal raised into the air and left without any support immediately falls. But, to consider the matter _a priori_, is there anything we discover in this situation which can beget the idea of a downward rather than an upward, or any other motion, in the stone or metal? In a word, then, every effect is a distinct event from its cause. It could not, therefore, be discovered in the cause, and the first invention or conception of it, _a priori_, must be entirely arbitrary. And, even after it is suggested, the conjunction of it with the cause must appear equally arbitrary, since there are always many other effects which to reason must seem fully as consistent and natural. In vain, therefore, should we pretend to determine any single event, or infer any cause or effect, without the assistance of observation and experience. Hence, we may discover the reason why no philosopher who is rational and modest has ever pretended to assign the ultimate cause of any natural operation, or to show distinctly the action of that power which produces any single effect in the universe. I say, then, that even after we have experience of the operations of cause and effect, our conclusions from that experience are _not_ founded on reasoning, or any process of the understanding. The bread which I formerly ate nourished me; that is, a body of such sensible qualities was at that time endued with such secret powers; but does it follow that other bread must also nourish me at another time, and that like sensible qualities must always be attended with like secret powers? The consequence seems nowise necessary. At least, it must be acknowledged that there is here a consequence drawn by the mind, that there is a certain step taken; a process of thought, and an inference which wants to be explained.