Kathy asked:

Can you please give me a basic definition for rationalists and empiricists?

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A "basic" definition is no problem — but not helpful either. In our context, the terms "rationalist" and
"empiricist" are used in relation to philosophers only and not in relation to an everyday approach to
life. The typical "rationalists" in the history of philosophy are Descartes, Spinoza, Leibniz. Their style
of philosophizing is what has later been dubbed "armchair-philosophy": You sit in your chair and think
on "first principles" and "necessary conclusions" holding the world together. Then comes the
empiricist down the lane and asks, if you ever checked your splendid ideas against the brute facts.
How could Newton's "law of gravitation" of 1678 ever have made such an enormous impact on the
whole of European thinking, if he had not shown that from his simple formula of gravitational forces
sprang the elliptical form of the orbit of planets that Kepler had derived in his famous laws some 70
years previously. And who forced Kepler to formulate those orbits? That was Tycho Brahe with his
extremely exact observations of those orbits — which was of course empirical. Since Antiquity the
idea has been that the orbits are circles, but Brahe's data excluded this possibility for the orbit of Mars
definitely in the same way as Michelson some 300 years later excluded with his extremely exact
measurements the possibility of the 'ether'.

Popper's concept of "falsification" sprang from his insight that Einstein's theory of General Relativity
could be disproved by the measurements of Eddington in the 1920s, but the theories of the Marxists
or the Freudians or the Christians could not. Many people do not even understand the concept of
"falsification". It does not mean to show that a proposition or a theory is false, but that there could be
devised an experiment (empirical!) that by its outcome conclusively "approves" or disproves the
proposition or the theory. Even the word "approves" is correct here, since no experiment can "prove"
a theory. Einstein's theories have up to now resisted all attempts to disprove or "falsify" them, but that
does not prove them to be right.

In the late 50s Heisenberg devised a "world-formula" for particle-physics from theoretical
considerations ("rationalist"), but then came the "quantum-chromo-dynamic" with its "quarks", and to
get there one had to build the large colliders costing billions of dollars ("empiricist"). But of course one
needs convincing theoretical concepts to make the investment of billions of dollars for the colliders
plausible. Even Columbus needed his (false) convictions on the distance to "India" in the west to find
support for his endeavour to get there. And the steam-engine of James Watt has not been the
outcome of "practical engineering" either: He had to improve a demonstration model of some older
type of steam-engine for the physics department of the University of Glasgow — then one of the best
universities of the world. There he chatted during the coffee-breaks with some of the most famous
physicists and chemists of the time and made use of their hints and suggestions on latent heat etc.
for his design of the new steam engine.

Locke and Hume are known as "empiricists" ("nothing is in the mind, what not has been in the
senses"), but Kant — who was well acquainted with the work of Descartes and Leibniz — got to his
decisive new insights by combining "rationalism" with "empiricism". It was Hume who got him up from
his "dogmatic slumber" by the notion, that "consequence" is not and cannot be an "empirical" concept
but must be a "postulate" of our thinking that transforms a mere empirical "sequence" into a
theoretical "con-sequence". As the examples above with Einstein, Heisenberg, Kepler and Newton
have shown, one always has to combine a theory and empirical data to get at useful results.

The rationalist approach had much to do with the remnants of christian Neo-Platonism in Occidental
thought. If human intelligence and the laws of nature are both expressions of the creative wisdom of
God, then by this common origin the workings of nature and human insight should fit by some sort of
inspiration. But Kant didn't need such an assumption. For his christian contemporaries that was
shocking, since then the old assumption of a unity of mankind and nature under god was not assured
anymore. Nature became a mere object for human technical and economical interests, it changed
from a world to live in to a mere resource to be explored and exploited. Since then the principle of "R
& D" — research and development — prevails: Theory, experiment and application combined to the
modern "instrument of progress" and the antagonism between "rationalists" and "empiricists" of the
time from about 1630 to 1780 has become historical.

Rationalism was no sort of stupidity though! The great rationalists have been great mathematicians
and logicians. They hoped to get at the core of the machinery of the universe by mere logical and
mathematical thinking since they held God himself to be the great "watchmaker" and mathematician
of the world. This was a great idea in the neo-platonic tradition. And then they were convinced in the
same line of argument of a deep reaching unity of truth, beauty and goodness respectively of reason,
sensitiveness and virtue. This unity has been the guiding idea of Spinoza (1632-77) and of Lord
Shaftesbury (1671-1713) and their time. This explains why one expected from rationalism much more
for the progress of mankind than we can imagine today. Even the slight contempt, with which
continental philosophers look on the anglo-saxon "empirical", "pragmatist" and "analytical" tradition of
thought springs from this "neo-platonic" and "rationalistic" concept of "the great order of things" (or
The Great Chain of Beingas Arthur O. Lovejoy has called it in his famous book of 1933, which is still
available).

One last remark on the sort of "experience" the English "empiricists" are talking of. This experience is
restricted to "sensual data" from which "concepts" and "theories" are derived. It's a strict
methodological sort of problem — to explain how "concept-formation from experience" takes place in
the human mind. Therefore the sneering remark of a French writer, those tea-sipping English
philosophers could not have the slightest idea of "real" experiences with deep love and deep faith and
deep mourning, with doubt, despair and commitment, totally misses the point. Philosophy is about
arguments, not about feelings.

Hubertus Fremerey

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