Imagine a very large fruit basket filled with every type of fruit. If you were asked to divide its contents into different categories, there would be various ways in which you could approach that task. There would be no right way of doing this. It would all depend on what the person asking you to make the categorisations had as their criterion for division. You could divide all the fruit into groupings such as citrus and non-citrus, or tropical and non-tropical. Or you might divide the fruits according to colour, putting all those that are orange in one category, all those that are green in another, and so on. You could divide up the contents of the basket according to the shape of the fruit, or its country or continent of origin.