What there is to learn

If we are to 'lay out the options' (as we expressed it earlier) of what there is to learn, the question at once arises of what categories to use. One point must be ceded in advance: that categorizations or taxonomies derive part (not all) of their merits or demerits from the purposes they are intended to fulfil. It is clearly possible—i.e. not logically contradictory or even lunatic—to set up more or less any set of categories, provided they are clear and their items discrete. We could consider various Xs to be learned in terms of their cost, the availability of people to teach them, the difficulty or interest experienced by various types of pupils in learning them, their 'relevance to the modern world' (whatever that may mean), the likelihood of getting grants to do research on them, or even the letters of the alphabet with which their titles began. Clearly much depends on what one is setting up the categories for; and few if any criteria could not be imagined to have some purpose (to take the last and apparently most absurd example, the compilation of an encyclopaedia).