Modern Logic and Real Reasoning

The various ‘impulses to philosophy’ which are the subject of this series of lectures, include a fascination with the general process of reasoning and argument—with the ‘game of logic’. We are all aware of the importance of reasoning in our lives and how difficult it can be to tell ‘good’ reasoning from ‘bad’. For example, which of the following are good arguments

1. (a) Some people have solved their own unemployment problem by great ingenuity in searching for a job or by willingness to work for less, so everyone could do this.

2. (b) Only gold will silence him. Gold is heavy. Therefore only something heavy will silence him.

3. (c) All red boiled lobsters are dead and all dead red lobsters are boiled, so all boiled dead lobsters are red.

4. (d) ‘The Brahmins assert that the world arose from an infinite spider, who spun this whole complicated mass from his bowels, and annihilates afterwards the whole or any part of it, by absorbing it again and resolving it into his own essence. Here is a species of cosmogony which appears to us ridiculous because a spider is a little contemptible animal whose operations we are never likely to take for a model of the whole universe. But still, here is a new species of analogy, even in our own globe. And were there a planet wholly inhabited by spiders (which is very possible), this inference would there appear as natural and irrefragable as that which in our planet ascribes the origin of all things to design and orderly system and intelligence. … Why an orderly system may not be spun from the belly as well as the brain, it will be difficult … to give a satisfactory reason.’ (David Hume, Dialogues on Natural Religion)