The excerpt from David Hume's, Dialogues on Natural Religion is structured as follows: Hume begins by stating an argument for the existence of God through the character of Cleanthes and then offers three criticisms of the argument through the character of Philo. The main argument that Cleanthes presents to Philo is as follows: (Premise) Nature is similarly structured therefore it works perfectly in tune like a machine or an invention. Working beyond human capabilities, therefore its creator must be one of high intelligence and infinite perfection.
(Conclusion) Cleanthes concludes his argument with the claim that God exists. Thefirst point that Philo makes of Cleanthes argument is that his premise is false. Philo says "If we see a house or a ship or a machine, we conclude, with the greatest certainty that it had an architect or builder; because this precisely that species of effect, which we have experienced to proceed from that species of cause". Therefore the similarity is not entirely reliable. As it is stated in the following "But wherever you depart, in the least, from the similarity of the cases, you diminish proportion ably the evidence; and may at last bring to it a very weak analogy, which is confessedly liable to error and uncertainty''Now what Philo means by this is that every time something happens in nature we come to conclusions, without studying the similarities between cases, we eliminate evidence for these similarities to be a hundred percent reliable.' 'For example, after having experienced the circulation of the blood in human creatures, we make no doubt that it takes place in Titius and Maevius: but from its circulation in frogs and fishes, it is only a presumption, though a strong one, from analogy, that it takes place in men and other animals. The analogical reasoning is much weaker, when we infer the circulation of the sap in vegetables from our experience.