Hyphens are used to connect words. One of their main functions is to reduce confusion in the meaning of words. In the past they were used far more often than we use them today and some words lose their hyphens through common usage, so there are no longer hard and fast rules (e.g. co-ordinates has now become coordinates). However, they are still a very important part of our language and their correct usage forms part of the KS2 English Grammar targets.