Why do some tunes sound catchy and memorable, others just bland, and others confusing? Are there rules that determine a good melody? It seems we have unconsciously decided that there are, because similarities in the way notes are used can be found between melodies composed in very different times and styles. For one thing, we establish a sense of key from the number of times the various notes in a scale are used during the course of a tune. And most tunesmiths tend to use sequences of notes that have many more small steps between successive pitches than large ones. Small steps help to bind the notes together into a coherent whole, whereas large jumps in pitch are apt to break a melody apart. There are ways of making that fragmentation less likely, such as using large jumps only on notes that last longer. Tricks like this are essential for injecting interest and liveliness into a tune. The art of writing a good tune lies partly in understanding the rules, even if only intuitively, and then judging how far they can be stretched.