As the overview article noted, Müller opened his first lecture with a bold declaration: “the science of language is one of the physical sciences.” At the time, this wasn’t merely a classification detail — it was a stance.

The era’s way of dividing knowledge

In nineteenth-century Europe, human knowledge was broadly divided into two kinds: physical science (botany, geology, anatomy — disciplines studying “the works of God”) and historical science (art history, legal history, the history of religion — disciplines studying “the works of man”). Müller himself states the distinction plainly in his lecture:

There are two great divisions of human knowledge, which, according to their subject-matter, may be called physical and historical. Physical science deals with the works of God, historical science with the works of man.

Which side does language belong to? At first glance the answer seems obvious. Language is something people speak, use, and reshape — surely, like art or law, it belongs to historical science. But Müller deliberately pushes back against this “obvious” answer.

Why call it a physical science?

Müller’s argument runs like this. No single speaker can change a language by whim. If an individual arbitrarily changes a word’s meaning or pronunciation, it means nothing unless other speakers pick it up. Language changes, Müller argued, according to its own laws, much as a plant grows or a crystal forms — beyond the will of any individual speaker. In this sense, language is less an “artifact of human will,” like a painting or a law code, and more “an object of observation and law,” like geological strata or plant growth. Even the name “comparative philology” (the era’s term for comparative language study) is misleading, he argued — the subject really ought to be studied by the same method as botany or geology.

Historical science Art, law, religion "Works of man" Language seems to belong here? Physical science Botany, geology, anatomy "Works of God" Müller placed language here instead His grounds: language changes by its own laws, beyond any individual speaker's will
Is language "the work of God" or "the work of man"? Müller's position. Diagram: ToL

A declaration that caused a stir

This stance naturally provoked strong pushback. Its most persistent critic was the American linguist William Dwight Whitney. Whitney argued that language is, fundamentally, a social institution, sustained by the agreement and convention of its speakers — and that treating it as a “natural” phenomenon detached from human will and history was simply a mistake. The argument dragged on for decades; in 1892, eight years before Müller’s death, Whitney devoted an entire book to the rebuttal, titled, pointedly, Max Müller and the Science of Language: A Criticism.

Which side was “right” is still not fully settled — modern linguistics accepts both that language change proceeds by regularities beyond any speaker’s individual will (the side Müller emphasized) and that language is a product of social convention (the side Whitney emphasized). But there’s no question that Müller’s provocative declaration was the first thing to turn “what does the discipline of linguistics actually do” into a subject of public argument.

Summary

PointContent
Müller’s claimLinguistics belongs to physical science, not historical science
His groundsLanguage changes by its own laws, beyond any individual’s will
Chief criticWilliam Dwight Whitney (argued language is a social institution)
How the argument settledModern linguistics accepts both sides as partly right

In a nutshell — Müller took a question that sounds dry but is actually fundamental — what is linguistics, really — and deliberately staged it as a provocation, on the very first day of his lectures. Whichever side turns out to be right, the sheer act of arguing the question openly in front of the public is what gave these lectures their force.