Albertus Magnus

The teaching

Taught from his own books on nature, above all On Minerals, On Plants and On Animals.

What nature does by her own causes

Albertus draws a clear line at the start of natural science. In studying nature, he writes, we do not ask how God the Creator, by his free will, uses his creatures to work miracles and show his power; we ask what nature, by the causes within it, can bring about. God can do anything, but the student of nature studies what nature does, and he holds both truths without confusing them.

Experience alone makes certain

In such matters, he says, experience alone gives certainty. A thing seen once is not proved: a sound observation is made many times and under every condition before it is trusted. So he sets beside what the old books say what he has seen himself, what others told him and who they were, and what he has tested and found false. It is said that the ostrich eats iron; he offered iron to ostriches and they would not take it, though they swallowed stones.

A statement does not become true by being written down. Whoever believes that Aristotle was a god, he says, must believe he never erred; whoever believes he was a man knows that he could err as we do. The student honours the old authors by checking them, wherever what they describe can be gone and looked at.

How metals are born

Metals grow in the veins of the earth from two things: a moist, flowing vapour, which is quicksilver and gives them their matter, and an earthy, fatty vapour, which is sulphur and works on that matter as a seed works. Joined in the earth and cooked by the heat of the place, they become metal, and the metals differ by the purity of the two and by how well the cooking went. Gold is the most perfect, made of the purest quicksilver and the finest sulphur in the best cooking; the base metals are the same work left impure or unfinished.

Art can help nature

Alchemy, if it is to be true, must follow nature: it must cleanse the quicksilver and the sulphur and cook them as the earth does, for art can help nature but cannot take her place. The alchemists who only tint a base metal yellow with sulphurous waters, or whiten it with arsenic, change its colour and not its kind, and their gold is gold to the eye alone. The test of a metal is the fire, again and again, and no art passes it by colour.

The powers of stones

Stones have powers beyond anything their elements explain: the magnet draws iron, and the lapidaries tell of gems that guard, heal or reveal. Albertus holds that such a power comes from the stone's form, which the heavens give it in the place and hour of its making, and not from any spirit dwelling in it. He gathers what the older lapidaries say of each gem, the sapphire, the emerald, the jasper and the rest, and keeps apart what he has tried from what is only told. Pictures sometimes found inside stones he explains by the vapours and the heavenly powers that shaped them.

This is the lore of stones as the thirteenth century held it, taught as what he says. A stone is no treatment, and its virtues are not a reason to delay seeing a doctor.

Natural magic and its limit

Natural magic, the use of the hidden powers that things have by nature, is lawful in his eyes; the calling up of demons is not. The Mirror of Astronomy draws the line among images, the figures cut in stone or metal under chosen stars. Some are abominable, made with fumes and invocations offered to spirits; some are detestable, made with written characters and names by which spirits are bound; and some take their power only from the figure of the heavens at the hour of their making, and these alone it allows.

The study of the stars is honest, for the heavens act on bodies. But they incline and do not compel, and a wise man can go against what his stars incline him to.

Plants, part by part

On Plants teaches the student to describe a living thing part by part: root, stem, bark, branch, leaf, flower, fruit and seed, and how each changes through the year. A plant has a soul of the lowest kind, the power to feed, to grow and to bring forth its like, but no sense and no movement of its own. He sets his descriptions of the plants he knew beside what he had read, and treats the cultivated garden as well: how grafting, manuring and pruning change a plant, so that a wild tree can be made gentle and a sour fruit sweet.

Animals and their judgement

On Animals adds to Aristotle what he saw for himself, from the whales and fish of the northern seas to the ways of eagles and bees, with a whole treatise on falcons: how they are kept, trained and healed. Animals have a power of judging what helps and what harms them, which makes a sheep flee a wolf it has never seen before, but they do not have reason. Reason is the mark of the human being, who alone can know the causes of what he sees.

His counsel to the student is the same throughout: look for yourself, compare, ask who saw it, and do not believe a thing because it is old.