Three centuries ago, when Isaac Newton recorded his timeless laws of motion, he likely never imagined that they would still be debated today.
Written in Latin, Newton’s principles outlined three universal laws describing the motion of objects in the universe. These principles have been translated, copied, and debated for centuries.
However, according to a philosopher of language and mathematics, we may have slightly misunderstood Newton’s precise wording in his first law of inertia.
A Mistranslation
Philosopher Daniel Hoek from Virginia Tech (USA) aims to “shed light on the truth” after discovering an “awkward” translation in the 1729 English version of Principia, Newton’s seminal work.
Based on this translation, countless scholars and teachers have interpreted Newton’s first law of inertia as stating that an object will remain at rest or in uniform straight-line motion unless acted upon by an external force.
This interpretation seems reasonable—until we recognize that external forces are always present, a fact Newton undoubtedly considered when formulating his definition.
Upon reviewing historical archives, Daniel Hoek found that the common interpretation of the law of inertia might be incorrect. It wasn’t until 1999 that two other scholars noticed an overlooked Latin word—“quatenus”, which means “insofar as”, rather than “unless”.
This mistranslation led to the misunderstanding that the law of inertia refers only to objects remaining in their state in the absence of external forces. However, Newton actually intended to emphasize that all changes in motion are caused by external forces.
“By restoring the word ‘insofar as’ to its correct position, scholars in 1999 recovered one of the fundamental principles of physics,” Hoek explained in a blog post.
The Debate
Daniel Hoek published his research in Philosophy of Science in 2022. However, this crucial correction has yet to be widely accepted. Even now, the old translation persists due to centuries of repetition and widespread adoption.
Some scientists argue that Hoek’s reinterpretation is too different from the traditional understanding. Others find it so obvious that it is not worth debating.
To the general public, both translations may seem similar in meaning. Hoek acknowledges that this reinterpretation does not change the essence of physics but provides deeper insight into Newton’s thought process when drafting the law.
“There has been much debate over the true nature of the law of inertia,” Hoek explained.
If we accept the conventional translation—that an object moves in a straight line until an external force alters its motion—then the question arises: Why would Newton write a law about objects unaffected by external forces when such conditions do not exist in our universe, where gravity and friction are always present?
Philosopher George Smith of Tufts University, an expert on Newton’s writings, stated: “The core meaning of the first law is to infer the existence of force.”
In fact, Newton provided three specific examples to illustrate this law. The most notable one, according to Hoek, is a spinning gyroscope. As we know, a gyroscope slows down in a spiraling path due to air resistance.
“By presenting this example, Newton made it clear how he understood the first law: it applies to accelerating objects under the influence of force—in other words, to objects in the real world,” Hoek asserted.
Hoek believes that this new interpretation clarifies one of Newton’s most fundamental ideas—a truly revolutionary concept at the time. It established that planets, stars, and other celestial bodies follow the same physical laws as objects on Earth.
“Every change in speed and direction is governed by Newton’s first law,” he said.
This discovery not only alters our perspective on physics on Earth but also makes us feel more connected to the vast universe.
