To humans, learning is like breathing–it comes naturally. What a human learns, however, is not natural and depends on the needs of the individual, the time she lives in, and what is available for her to learn.
A thousand years ago, ‘book’ knowledge was the province of the Church and of the elite (usually male). Over the next two hundred years, formal education became more widespread. Cambridge University, for example, was founded in 1209 by a group of men dissatisfied with Oxford. When a man went to the university, his education began with the seven liberal arts: Latin grammar, rhetoric, logic, arithmetic, geometry, astronomy, and music. After he received his Master of Arts, he could choose to study law, medicine, philosophy, or theology, upon which he would receive his doctorate.
Knowledge, however, is not necessarily just ‘book learning’. While this afternoon my son spent twenty minutes explaining to me the difference between a star, a white dwarf, and a black hole (which had him very excited), this kind of knowledge has limited use in daily life. In the Middle Ages, the ‘average’ person, might not have been able to read a book, but he still might have an encyclopedic knowledge of arts and sciences about which a modern person knows nothing: herbal remedies, swordmaking, blacksmithing, wine making, crafting of soap, animal husbandry, how to sheer a sheep, card wool, spin thread, weave, sew by hand, make cheese, ride a horse . . . the list is endless. Most twenty-first century people would be as completely helpless when instructed to cook a meal in the Middle Ages (beginning with how to start a fire without matches) as a medieval person would be when faced with a computer.
It is likely that individuals of each era would find citizens of the other woefully ignorant.
There is an additional issue, however, of the tools a person has to think with. A person who has never been exposed to philosophy–whether scientific, theological, post-modern etc.–is not able to analyse an argument, to follow a progression of logic, or tell the difference between coincidence and causality. And for this reason, the ability to read and write, if nothing else, gives an individual access to knowledge and different ways of thinking which illiteracy does not provide. It is not that modern people are ‘smarter’ or ‘less ignorant’. What we have is access. We live in a society in which knowledge–whether individual or societal–can be passed from one generation to the next–to accumulate and expand–because so much is written down. And not only is it written down, but easily accessible to a virtually the entire population. This, more than anything else, is the advantage that modern people have over their medieval ancestors.