Hi, I'm Peter Adamson and you're listening to the history of philosophy podcast brought to you with the support of the philosophy department at King's College London and the LMU in Munich online at history of philosophy.net.

Today's episode just adds salt, paracelsis and alchemy.

Pre-modern science does not have the best of reputations. The mere mention of the topic calls to mind the use of leeches and the belief that the sun goes around the earth.

So historians of science have had to find ways to explain why we shouldn't just ignore everything that happened before, say the 17th century.

Specialists in pre-modern medicine might tell you of amazing breakthroughs made long ago, the discovery of the nervous system in Alexandria in the 2nd century BC, or successful eye surgery being done in the Islamic world.

They might even suggest that we still have something to learn from long dead scientists. The modern doctor would do well to heed gallons advised to treat patients holistically, considering their personal history, diet and exercise regime, mental state and individual constitution.

While these moves might be persuasive in the case of medicine, they seem less promising when it comes to the disciplines known by the disparaging name of pseudo sciences applied to such disciplines as astrology and alchemy.

Most people assume that both enterprises were a fanciful waste of time, and experts in their history have to work hard to convince even academic colleagues that they are worthy of study.

Often they do so by pointing out that we still take astronomy and chemistry seriously, and that these two sciences were intimately bound up with their pseudo-scientific counterparts.

When it comes to astrology, it suffices to mention Ptolemy, a near contemporary of gallons, who was the greatest ancient authority on both astral observation and astrological predictions.

As for alchemy, it's surprising to learn how recently it was first distinguished from chemistry. We can find skepticism about the claims of alchemists going back as far as the history of alchemy, specifically as to whether they could really turn base metal into silver and gold.

But it was only in the middle of the 17th century that these critics drew a contrast between a spurious art called alchemy and a genuine science called chemistry.

In fact, they are really just the same word. The al, at the beginning of alchemy, is just the Arabic definite particle al, at the front of alchemyah, which was in turn borrowed from the Greek word kemeah.

Early modern scholars engaged in some pseudo-science of their own here, offering bogus etymologies, including one deriving the syllable al from the Greek word haus, meaning salt.

As it happens, salt is going to be a main ingredient of the story I tell in this episode. But before we get to that, we should go beyond etymology to consider that there was good reason for pre-modern scientists to believe in alchemy.

While alchemists couldn't actually make gold or silver, they could do a lot of other things. They identified many minerals and chemicals, mastered techniques like distillation, which enabled them to extract pure alcohol, and developed processes for separating metals from one another.

That included the isolation of precious from base metals, which could easily be confused with actually producing the precious metal.

The same impression could be given by inducing a tincture in a non-precious metal to make it look like gold or silver.

Then, too, the possibility of alchemy was well-founded in more general theories of nature. For Aristotle and his many followers, all bodily substances were ultimately made from the four elements, air or a firing water.

Aristotle explicitly said that these elements can turn into one another, as when water evaporates to become air.

It seems to follow that it should be possible to break down any physical substance, led, for instance, into its elemental constituents and to use these as the basis for making another substance, like gold.

Here, it's telling that when the Muslim Aristotelian Al-Farabi wrote a short work that is critical of alchemy, he conceded that in principle anything can be turned into anything.

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