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Philosophy 024: Big Ideas Prof. Robert DiSalle ( ) Talbot College 408, 519-661-2111 x85763 Office Hours: Monday and Wednesday 11:30-12:30 PM Course Website: The idea of a scientific method What is so great about science?

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Philosophy 024: Big Ideas

Prof. Robert DiSalle (

Talbot College 408, 519-661-2111 x85763

Office Hours: Monday and Wednesday 11:30-12:30 PM

Course Website:


The idea of a scientific method

What is so great about science?

Does science have a way of looking at the world that makes it superior to other ways in which humans look at the world?

Is science more objective than other ways of thinking?

Does science have a better grasp of the truth than other ways of thinking?

Is there really a scientific method?


The Cartesian idea of method:

To arrive at indubitable truths by conducting the reason correctly

Everything that is true should be deducible from the fundamental truths that are discovered by reasoning

Galileo’s idea of method:

To reach the truth about the sensible world by the study of natural phenomena

To use mathematical ideas to describe precisely how nature behaves



Reason should be able to reveal the underlying causes of all physical phenomena


Reason can’t anticipate how the physical world must be, but must prepared to be surprised by what empirical study will reveal.

Combining mathematical and empirical reasoning will enable us to describe how nature behaves-- not necessarily why.


Galileo’s conflict with the Church: Can questions about the natural world be settled by the Bible? Or must they be settled by the best empirical and mathematical methods of science?

Are we free to investigate nature, or must we be constrained by religious authority?

The book of God: The history of God and his creation, written in a language for general human comprehension

The book of Nature: The natural world itself, revealing its laws in the phenomena--

--but written in the language of mathematics.


“Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But this book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth.”



Galileo’s Abjuration before the Inquisition, 1633

…because I have been enjoined, by this Holy Office, altogether to abandon the false opinion which maintains that the sun is the center and immovable, and forbidden to hold, defend, or teach, the said false doctrine in any manner… therefore, with a sincere heart and unfeigned faith, I abjure, curse, and detest the said errors and heresies, and generally every other error and sect contrary to the said Holy Church; and I swear that I will never more in future say, or assert anything, verbally nor in writing, which may give rise to a similar suspicion of me; but that if I shall know any heretic, or any one suspected of heresy, I will denounce him to this Holy Office, or to the Inquisitor and Ordinary of the place in which I may be.


Galileo on science and Scripture:

I think it would be the part of wisdom not to allow any one to apply passages of Scripture in such a way as to force them to support as true any conclusions concerning nature, the contrary of which may afterwards be revealed by the evidence of our senses, or by actual demonstration. Who will set bounds to man's understanding ? Who can assure us that every thing that can be known in the world is known already ?


Galileo on science and Scripture (continued)

. . . I am inclined to think that Holy Scripture is intended to convince men of those truths which are necessary for their salvation, and which being far above man's understanding cannot be made credible by any learning, or by any other means than revelation. But that the same God who has endowed us with senses, reason, and understanding, does not permit us to use them, and desires to acquaint us in another way with such knowledge as we are in a position to acquire for ourselves by means of those faculties— that, it seems to me I am not bound to believe…


Galileo vs. the Aristotelians on method:

Science can never appeal to the authority of any text, no matter how great the philosopher who wrote it.

Aristotle himself did not accept the authority of anyone, but judged for himself the opinions of his predecessors.

In matters of natural science, Aristotle himself never appealed to authority, but relied on the evidence of his senses.

If Aristotle were alive in Galileo’s time, he would not believe what he wrote in 350 BCE, but would revise his views on the basis of all the accumulated evidence.


Galileo vs. the Aristotelians on the natural world:

The earth is not unique in the universe, and the celestial bodies are made of the same basic stuff.

Falling to the earth is not a simple and natural motion, but a compound of two motions, horizontal and vertical.

Because motions can be combined, we cannot tell whether the earth is moving by observing bodies falling on it.

Speed of falling doesn’t depend on the weight of the body, but is the same for all bodies.


Why dropping a stone from a “stationary” tower is like dropping a stone from the mast of a moving ship


The lesson of falling bodies:

We must rely on our senses, but it is a mistake to take what they tell us at face value.

“The stone falls straight from the top of the tower to the bottom” : that is not a statement of fact!

It is an interpretation of what we see.

If the earth is at rest, the stone falls in a straight line. But if the earth is moving, the stone is falling in a parabola.

Science requires the combination of observation with mathematical reasoning.


Some simple ideas about scientific method

Inductivism: Science proceeds by performing experiments repeatedly, and accumulating observations.

Then it makes inductive generalizations from the accumulated facts. These are the laws of science. (Francis Bacon)

Hypothetico-Deductivism: Science proceeds by devising hypothetical models for how nature might really be organized. Then it deduces the consequences of these models, and compares them with observation. (Christiaan Huygens)


Kant’s questions about scientific method:

How has science achieved universal assent, while philosophy is the subject of endless dispute?

What distinguishes scientific reasoning from philosophical reasoning, so that the former leads to principles that are necessary and universal, whereas the latter remains arbitrary and particular?

How can philosophy start on “the secure path of a science”?


Kant’s “Copernican Revolution”:

The laws of nature don’t describe the way things are in themselves; they describe conditions that our understanding imposes upon experience.

“Every effect has a cause” is not a truth about things in themselves. If it were, we would be right to doubt it.

Instead, it is a rule that the human understanding imposes on the appearances, in order to submit them to a rule.

Without such rules experience would be impossible. The world would be a chaos of sensory appearances.


Kant: Scientists like Galileo “comprehended that reason has insight only into that which it produces itself after a plan of its own...for otherwise, accidental observations, wth no previously fixed plan, will never be made to yield a necessary law….”

“Reason, holding in one had its principles…and in the other hand the experiments it has devised according to those principles, must approach nature in order to be taught by it. It must not, however, do so in the manner of a pupil, who agrees to everything the teacher says, but of an appointe judge, who compels the witness to answer the questions which he himself has phrased…”


The Newtonian method:

Instead of making up theories to explain the facts, compel the facts to answer theoretical questions.

Example: Use the laws of motion to impose questions on the world, such as, “what forces are at work?”

If the laws are assumed to be true, then every acceleration that we see is telling us something about a force.

(F = MA, or “force equals mass times acceleration”: this means that forces cause accelerations, and accelerations reveal the action of a force.)


Newton’s laws of motion (The Mathematical Principles of Natural Philosophy, 1687)

Law 1. Every body, left to itself, maintains its state of uniform motion or rest until acted upon by a force.

Law 2. Acceleration is in the direction in which a forced is impressed, and is proportional to the magnitude of the force and the mass of the body.

Law 3. To every action there is an equal and opposite reaction.


Newton’s discovery of universal gravitation:

The accelerations of the planets answer all of our questions about the masses and the forces that move them:

What is the magnitude of the force?

What is the center of the force?

What body exerts the force?

Where is the centre of mass of the system?


Kepler’s area law: The radius drawn from the sun to a planet sweeps out equal areas in equal times.


Kepler’s “harmonic law”: The periodic time t and the mean radius r of any planetary orbit are related as t2 r3.

Or,t r3/2

Or, for any two planets a and b,

Ta2 / Tb2 = Ra3 / Rb3


Because (by Law I) a body should naturally recede from any curve along the tangent, the closed orbits of the planets should tell us that a force is maintaining them in the curve, and should tell us something about the magnitude and variation of that force.


The discovery of universal gravitation:

From the accelerations of the planets we infer:

The force holding them together is inverse-square, i.e. proportional to 1/r2 (r is the radius of the orbit)

The force is directed to the sun, and the force on the moon is toward the earth (and Jupiter’s moons to Jupiter, etc.)

The centre of mass is very close to the sun, since the sun has most of the mass of the entire system.

The interplanetary force is the same as gravity, since gravity is the same as the force that holds the moon in orbit around the earth. (The falling of an apple is the same as the falling of the moon.)


From this we can infer that the earth revolves around the sun, rather than the sun revolving around the earth.

For all planets in the system revolve around their common centre of gravity, and that is always near the center of the sun.

The big question: What is really moving in the solar system? (i.e. who was right, Ptolemy or Copernicus?)

Before Newton: Choose the most reasonable hypothesis.

After Newton: Let the laws of physics turn this into an empirical question, and let the facts decide.


Centre of gravity: Where do you put the fulcrum in order to balance the sun against all the planets?



Answer: Because the Sun is so much more massive than all the planets put together, the centre of gravity is never far from the sun, even if all the planets happen to be on the same side.


To put the Earth in the centre makes as much sense as thinking that the Earth’s mass can balance all the other masses together.