Rationalism and Empiricism in Early Modern Philosophy and Physics
British Empiricism: Continental Rationalism:
Francis Bacon (1561-1626) - founder Rene Descartes (1596-1650)- founder
John Locke (1632-1704) Benedict de Spinoza (1632-1677)
Isaac Newton (1646-1727) * Gottfried Leibniz (1646-1716)
David Hume (1711-1776)
*Newton synthesizes some aspects of the two traditions; like Descartes, he
does see a major role for deduction and mathematical imagination in
constructing a unified mechanics (e.g., from Kepler’s three laws of planetary
motion, he deduced an equivalent single, more economical law; he posited the
law of universal gravitation from which middle principles, e.g., the law of
falling bodies, could be deduced).
Tenets of Empiricism: Tenets of Rationalism:
All ideas are derived from experience. Some of our ideas are innate.
Reason can analyze concepts and discover Reason can intuit some general
their logical relations, but reason alone truths about the world and can
cannot yield knowledge about the world deduce others from them, e.g.,
or what exists. Knowledge about the world for Descartes, one can intuit
and existents is based on sensory that every event has a cause, and
observations and inductive inferences one can prove God exists and
from them. that minds are immortal.
Bacon’s Empiricist Method of Science: from observations of particular
things and events, one moves to ever more general claims by enumerative and
eliminative induction. This is a bottom-up approach from a basis of particular claims based on
observations* to ever more general, abstract ones.
Most general principles: e.g., principle of inertia, law of universal gravitation
Middle principles: e.g., Kepler’s laws (e.g., all planets move in elliptical orbits
of which the sun is one focus), Galileo’s Law of Falling Bodies.
Lesser Principles: e.g., Mar’s orbit is an ellipse with the sun as one of its foci.
*Particular observations: e.g., how fast particular balls of different weights
roll down an incline; numerous observations of Mars over time from Earth
How should theology and science be related?
Empiricists agree that theological principles have no role to play in science.
(For instance, laws of nature cannot be known by inference from theological
For some empiricists, notably Bacon, scientific principles have no role to play
in theology either.
For other empiricists, e.g., Locke, Hume, and Newton, from knowledge about
the world, one can know with a high degree of probability whether or not God
exists; and, if there is a God, something about God’s nature (=divine
Locke accepted Bacon’s empiricist method of science. Rene Descartes (1596-1650) father of modern philosophy; founder of
1604-1612 studied logic, scholastic philosophy (with which he became
disillusioned), and math at the Jesuit college of La Fleche in Anjou
1616 earned law degree at Poitiers, then travelled in Europe, enlisted in the
Nov. 10, 1619 he had a dream or intellectual vision– it was his mission to
discover the unity of the sciences, to produce a single, coherent body of
- his first mission was to work out the relations between geometry and
algebra—he then laid the foundations of analytic geometry -- can convert
geometrical relations into algebraic formulae (much more economical way
to represent geometry) and represent algebraic formulae geometrically by
the Cartesian coordinate system
1628 – settled in Holland and did experiments in optics and physiology
1633 – had written a book called The World, which contained “all of physics”,
his theories and experiments on heat, light, astronomy, and human physiology Descartes withdrew the book when he heard of Galileo’s condemnation by the
1636 – had a daughter, did not marry her mother
1637 – Discourse on the Method written in French because Descartes said he
wanted literate, intelligent people who were not proficient in Latin, including
women, to read it
1640 – child died; Descartes said it was the worst blow of his life
1641 – Meditations on First Philosophy his most famous work, written in
Latin, later he approved a French translation
1643 correspondence with Princess Elizabeth of Bohemia
1644 Principles of Philosophy - Part II is his physics; dedicated to Princess
The Passions of the Soul – last work, inspired by discussions with Princess
1649 – went to Sweden to become tutor to Queen Christina, who insisted that
lessons be early in the morning
1650 - Descartes, who had always been sensitive to the cold, developed
pneumonia and died within a few months of taking up residence in Sweden Descartes’ (Cartesian) Rationalism:
Descartes loved the certainty of math and its structure as a series of sound,
valid, deductive arguments
- he wanted to devise a deductive system for all knowledge
Among his chief goals were
(1) To secure a solid foundation for knowledge, esp., for physics
(2) To show that physics, “the new mechanical philosophy”, is
compatible with the existence of God and the soul (to reconcile
science and religion)
The Need for a New Method
Like Bacon, Descartes believed that to achieve and expand knowledge, a new
method must be devised. His method, however, was radically different from Bacon’s and his view of the
structure of knowledge (where one begins, what is basic, how one builds up
knowledge systematically) is importantly different.
Descartes’ Tree of Knowledge (from Principles of Philosophy, p. 350):
Tree top: Branches of tree are specific fields: e.g., medicine, mechanics, and
ethics; these come last
Trunk of the tree is physics, including most abstract principles of nature
**Roots of the tree lie in metaphysics, including most abstract principles about
what exists, e.g., abstract principles of causation and truths about God
For Descartes, one proceeds from the most abstract, general principles to less
What would Bacon think of Descartes approach?
Bacon wrote, “...that method of discovery and proof according to which the
more general principles [of physics] are first established, and then the
intermediate axioms are tried and proved by them, is the parent of all error
and the curse of all science” (Aphorism lxix, p. 314).]
Descartes’ Quest for Certainty and Avoidance of False Beliefs
Devise a method to remove any false beliefs he might have acquired
Discover what, if anything, he could know with certainty or without
Suspend judgment about any claim of which he is not certain (even if it
is highly likely to be true) Method: Phase I -- discover if there are any indubitable propositions
Methodological Doubt: He believed that his beliefs were either (1) based on
reasoning from sense experience or (2) based on reason alone. If he could
shed doubt on sense experience and then reason, he would have shed doubt
on the entire sets of beliefs based on these two faculties.
Would he discover any indubitable propositions that could survive the
Method: Phase II -- Proceed by demonstrations to further truths
If he did discover any indubitable truths, he would use them as premises in
valid, deductive arguments by which he could proceed from the simplest
truths to more complex ones. In this way he would achieve demonstrative
knowledge just as one demonstrates the truth of complex theorems from
simple axioms and postulates in math by valid, deductive arguments.
If he (re)constructed his belief system in this way from indubitable truths and
proceeded by truth-preserving deductive validity, he would have a body of
beliefs he knew with certainty to be true.
Meditations- Descartes deploys his method
Meditation I Are there any propositions one can know without doubt or with
Consider the following propositions.
1. There is a world which I always perceive as it is.
[I have senses that always give me reliable information about the world.
or All of my beliefs about the world based on my sensations are true.]
2. I am now standing in this room.
[I am now awake and perceiving that I am standing in this room.] 3. There is a world which I sometimes perceive as it is.
[I have senses that sometime give me reliable information about the
world. or Some of my beliefs based on my sensations are true.]
4. 2+3=5; 2 is the only even prime number.
5. I exist.
Descartes’ Sceptical Arguments:
I. The Argument from Illusion: Various sensory perceptions are
inconsistent, e.g., a stick partially submerged in water looks
broken, but feels continuous; objects can look yellow to a person
suffering from jaundice.
How does one distinguish illusory from veridical experience?
Which of the above propositions does this argument bring into the
sphere of the doubtful? 1? 2? 3?
I’m not a lunatic. I know I’m not suffering from delusions/hallucinations
about my current surroundings. II. The Dream Argument: Yet, is it not possible that I’m dreaming
now, instead of awake sensing I’m standing in this room?
Typically dreams are incoherent, discontinuous, and break laws
of nature; but occasionally I have had realistic dreams. I have
believed I was standing in this room (seated in my chair at my
desk), but then waked up and discovered I had been dreaming it.
Hence, for all I know now with certainty, I might be dreaming I am
standing in this room. Hence, I can doubt proposition 2. I cannot
be sure I am awake now; there’s a slight chance I’m having one of
those realistic dreams right now.
Does the Dream Argument shed doubt on 3? Might I be “dreaming” all
How does Descartes argue for his answer to this question?
III. The Evil Genius Hypothesis
At this stage Descartes leaves the realm of ordinary experiences and familiar
grounds for doubts. He calls this “hyperbolical” doubt.
Suppose there is a very powerful, clever demon who deploys all of his
resources to deceive me. (At this point, I cannot be absolutely sure that
there is a good God who would not allow me to be deceived in this way.)
(a) Suppose this powerful evil genius is the source of all of my complex,
coordinated “sensations” which I have taken to be caused by the world.
Suppose I don’t have a body or senses, but what I have taken to be
experiences of a world is in fact all simulated experience—the evil
demon has given me faux sensations. [I have experienced a virtual
reality, but not a real world that I received information about through
my sense organs.] This hypothesis sheds doubt on 3.
(b) Suppose further this evil genius tampers with my reasoning so that I get
confused and make mistakes, but he makes me think that I understand
what I’m thinking or induces me to believe I have made valid deductions
from claims that seemed true.
It’s possible that I make mistakes when I believe I intuit mathematical claims
or prove theorems. Hence, I have shed the slightest doubt on the claims of 4.
How does Descartes distinguish objective from subjective certainty?
Is there any belief that the EGH does not render doubtful?
But I was persuaded that there was nothing in all the world, that there
was no heaven, no earth, that there were no minds, nor any bodies: was
I not then likewise persuaded that I did not exist? Not at all; of a surety I
myself did exist since I persuaded myself of something [or merely
thought of something]. But there is some deceiver or other, very
powerful and very cunning, who ever employs his ingenuity in deceiving
me. Then without doubt I exist also if he deceives me, and let him
deceive me as much as he will, he can never cause me to be nothing so
long as I think I am something. So that having reflected well and
carefully examined all things, we must come to the definite conclusion
that this proposition: I am, I exist, is necessarily true each time that I
pronounce it, or that I mentally conceive it.
Proposition 5. ‘I exist’ cannot be doubted whenever one entertains it. The proposition is self-verifying. The conditions under which one thinks it or
consider it are the conditions that make it true. This is a special property that
thinking ‘I exist’ has.
Descartes has found his indubitable truth.
He then asks what is this “I” which I know exists every time I reflect on it? I
am a thing that thinks—a thing that affirms, denies, doubts, imagines, wills,
desires, seems to sense. I am a mind or a thinking thing.
I have a numbe