Everyone knows that Formal Logic has something to do with argument or reasoning. Some think that it is a sophistic art, an art of winning arguments; others, nearer the mark, think that it is the more reputable sophistic art of reasoning correctly and spotting fallacious arguments when others use them; others, still nearer the mark, think of it less as an art or technique and more as an intellectual study of the structures of arguments or inferences, classifying them as sound or fallacious. We can get a good deal nearer the mark still by saying that Formal Logic is the study of the structures of propositions and deductive inferences. This remark is not offered as a definition of ‘formal logic’, but rather as an indication of the sort of subjects discussed in this book. Indeed it is not clear that any adequate definition of ‘formal logic’ (let alone ‘logic’) is possible – if you want to know what Logic is about, then you must set to work and do some. Let us get down to it.