Aristotle's Fallacy: Birth of Classical Physics with Galileo and Newton

Aristotle's Fallacy refers to a mistaken empirical observation from everyday life that an external force is continuously needed to keep an object in motion. If this force stops, the object will come to a stop. Based on this logical reasoning, Aristotle also argued that the natural state of any object is rest. Not motion. 

NCERT explains in the Laws of Motion chapter that the

“Aristotelian law of motion may be phrased thus: An external force is required to keep a body in motion.”

It's called Aristotle's Fallacy, as this observation that the object's natural state is rest is the opposite and incorrect to what Newtonian or classical physics proved about the motion of objects.   

First, if we define the meaning of fallacy, it refers to an incorrect argument. It may seem logical on the surface, but upon closer examination through critical analysis or experimentation, the logic falls apart. 

That’s precisely what happened with the Aristotelian law of motion. 

To repeat, Aristotle assumed that an object requires continuous force to maintain its motion. Otherwise, it stops moving. Because this law was grounded on the fact that the object or body’s natural state was rest. 

On the surface, this is also true. You can push a box, and the moment you stop moving it, the box remains still. This observation is logical. 

But Aristotle misinterpreted the effect of slowing down as a natural tendency of objects to come to rest.  Before Sir Isaac Newton disproved this, with his First Law of Motion, he mathematically proved that an object in uniform motion will continue moving unless there is an opposing force to stop it, while an object at rest will stay at rest. 

This was, however, Newton's predecessor, Galileo Galilei, who founded the principles of inertia, aka, the Law of Inertia, using experiments on inclined planes. 

The implication of Newtonian physics is twofold. 

• The motion of an object continues on its own. It doesn’t need a continuous push.
• If there’s no opposing force like friction or air resistance, the object keeps moving.

In short, Newton proved that the natural state of objects is uniform motion unless interrupted by force. Aristotle understood it the other way around, without accounting for different concepts such as inertia, friction, and force.

This is why we call it Aristotle’s Fallacy.

Here is a table for reference, you should take note of while answering questions on Aristotle’s Fallacy in your exams. 

Cause of Motion Stopping	Aristotle’s View (Fallacy)	Galileo’s Insight	Newton’s Contribution
Natural State of Objects	Rest is the natural state of every object. They stop moving if not continuously pushed.	Motion is typically an object's natural state if no opposing force exists.	An object will move continuously in a straight line unless an external force acts upon it.
Cause of Motion Stopping	If force is removed, motion stops.	It's friction that causes motion to come to a stop.	The First Law of Motion explains that inertia and net external force are behind the motion of objects.
Understanding of Force	You need a continuous force to keep an object moving.	Only a net force (like friction) can change an object’s motion.	Motion does not always require continuous force. A net external force can cause acceleration or deceleration of an object.
Role of Friction	Friction is not yet accounted for.	Friction is identified as the hidden force that causes motion to stop.	Friction can be quantified, and so can other forces that influence motion through the three laws of motion.

 

Here are some essential notes to revise if you feel you are stuck before your exams. 

Units and Measurements Class 11 Notes	Mechanical Properties of Solids Class 11 Notes
Motion in a Straight Line Class 11 Notes	Mechanical Properties of Fluids Class 11 Notes
NCERT Class 11 Notes for Motion in a Plane	Thermal Properties of Matter Class 11 Notes
Laws of Motion Class 11 Notes	Thermodynamics Class 11 Notes
Work, Energy, and Power Class 11 Notes	Kinetic Theory of Gas Class 11 Notes
System of Particles and Rotational Motion Class 11 Notes	Oscillations Class 11 Notes
Gravitation Class 11 Notes	Waves Class 11 Notes

Have a look at these as well. 

NCERT Class 11 Notes for PCM

NCERT Class 11 Physics Notes

 

Looking for NCERT Solutions for Physics Class 11? Here are chapter-wise NCERT solutions pages to practice with.  

Units and Measurements Class 11 NCERT Solutions	Mechanical Properties of Solids Class 11 NCERT Solutions
Motion in a Straight Line Class 11 NCERT Solutions	Mechanical Properties of Fluids Class 11 NCERT Solutions
Motion in a Plane Class 11 NCERT Solutions	Thermal Properties of Matter Class 11 NCERT Solutions
Laws of Motion Class 11 NCERT Solutions	Thermodynamics Class 11 NCERT Solutions
Work, Energy, and Power Class 11 NCERT Solutions	Kinetic Theory Class 11 NCERT Solutions
System of Particles and Rotational Motion Class 11 NCERT Solutions	Oscillations Class 11 NCERT Solutions
Gravitation Class 11 NCERT Solutions	Waves Class 11 NCERT Solutions