With medieval philosophy covered, it’s time
to examine the next big paradigm shift in philosophy. The 15th century Renaissance
marked the end of the medieval era and signaled a revival of ancient Greek knowledge
and values. Copernicus revolutionized astronomy by removing Earth from the center of the universe
to propose a heliocentric and more mathematically accurate model, thereby greatly influencing the
Scientific Revolution to come. Likewise, the “Divine” was taken out of the center of discussion
in philosophy and the sciences to shift the focus onto human beings in a natural world. Though by no
means atheistic, as many authors would emphasize their faith in some way, this period diverted to a
secular discussion in a naturalistic perspective. In philosophy, this shift was characterized by
two main schools of thought: the rationalists, focusing on reason itself and its faculties above
the senses and experience, and the empiricists, who, though not discarding reason entirely,
focused on experience and that which is attained by the senses, above a strong conception of
rationality. This contrast was similar to the already age-old distinction between Platonic
and Aristotelian conceptions of the world. Both schools were followed by the idealists,
who tried to resolve this duality in different manners. We’ll begin with the rationalists here,
then move on to the empiricists, and then follow up with the idealists. Finally, we’ll talk about
political philosophers, and then conclude this section on modern philosophy by catching up
on the logical developments in this period, before then advancing to contemporary
philosophy in the early 20th century. Interestingly, the first philosopher we will talk
about does not fit any of these labels. Michel de Montaigne was a curious figure in the 16th
century who created the “essay” format as we know it today in literature, also reviving Pyrrhonism
in modern philosophy, and being one of the first examples of the limitless manner of philosophical
investigation that the modern times allowed. He wrote an abundance of texts, all guided only
by a frank desire to understand human nature, education, and the world, through his own reason.
They were so forthright that he frequently changes positions on multiple topics throughout his life,
and thus he always remarked that as his own senses and memory are faulty, so are everyone’s.
Therefore no human being could ever achieve true knowledge of anything. His essays were deeply
affected by the expeditions to America being made at the time. Reports were given from voyagers
regarding a “New World”, not only in a physical sense, but also cultural, given the description of
costumes and worldviews from natives. These shaped Montaigne's views on culture and tolerance, and
he refused to accept an ethnocentric approach in which European culture was by any means superior
from those that could be found in the “New World”. He also wrote extensively against
authority and organized religion, as he judged the religious quarrels of his time
beyond any resemblance of divinity, and thoroughly criticized education of his time, which focused
on supposed absolute knowledge of the teacher. This prevented curiosity and questioning, and
thus learning itself. Additionally, there was the frequent use of abstract concepts distant from
students’ everyday lives and experiences. Although his ideas were not very relevant to future
philosophy, being so varied and inconsistent, his new method of writing and pedagogical
insights are clearly very relevant to this day. One of the first and most famous proper
rationalists was René Descartes, a prominent French philosopher and mathematician who created
the Cartesian coordinate system we are familiar with from algebra. Descartes wrote meditations
regarding existence and reason, toward finding the best method to discover the most fundamental
truths on which all systems of knowledge could rely upon. Mathematics, philosophy, ethics, and
everything else were all intertwined for him, symbolizing different aspects of the same reality,
creating a metaphor for a tree where mathematics, ethics, medicine, and other subjects would
be its branches, physics would be its trunk, and metaphysics, or ontology, its roots. Akin to
Plato, only through reason could we be able to understand all the parts of the tree and discover
its metaphysical, unchanging truths supporting everything else, for our reason allows us to
question everything in order to investigate the roles and connections between different objects
and concepts. To arrive at the ultimate truths, Descartes wondered about dreams, and how we tend
to believe everything within a dream is real right until we wake up. Couldn’t we then possibly be
inside a dream without knowing it? After all, bodily senses can frequently be mistaken, as when
your hand is cold and the water in a bowl seems hot when it’s just room temperature, or when you
mishear someone in a game of telephone; thus they cannot be fully trusted. He exaggerates this as he
posits a fictitious “evil genius” who is bent on fooling us at every turn, and thus everything that
can be questioned, can statistically be false, and as such cannot be a foundational truth to
base all valid knowledge. But what is the only thing that cannot be false? That would be the only
thing allowing for our capacity for questioning itself – as if it were false, we would not be able
to question anything. That one exists is the only thing a rational entity can be sure of without
any doubt. Reason, then, is the first ultimate, foundational truth, and from this realization he
coined his famous phrase “I think, therefore I am” – “I am” being used in the sense of “I exist”.
But if such absolute, unquestionable truth exists, then the Christian god is also true, for no evil
genius would grant us the capability of realizing their work is false. This is an ontological
argument, similar to that of Anselm, in that the existence of the Christian god is asserted
given an abstract logical necessity. From these basic truths, according to Descartes, one is able
to identify all the true laws governing nature. Some argue that the addition of the ontological
argument, and therefore the mention of God in his argument, was there only to avoid censorship
from the Catholic Church, given that the argument can work even without God – but this is highly
debatable. So, however far Descartes veered from theology, the divine is still strong in his
work as a foundational element. He then went on to defend a dualist metaphysics, in that
we have the sphere of things of the mind (res cogitans) and the realm of bodily experience
(res extensa), two coexisting but essentially different substances. But only humans, as his
god’s creations, would be endowed with reason, other animals being nothing but automatons living
their life mechanically toward survival, unaware of the logical threads governing existence.
Though Aristotle and others established general guidelines for scientific endeavors, the method
Descartes developed as a manner of inquiry toward these fundamental truths is one of the first
“official” formulations of what would become the current scientific method. The four steps may
be summed up as follows: 1) question everything which is not self-evident, 2) divide everything
into the smallest, simplest parts possible, 3) solve problems going from simplest to
most complex and 4) reexamine the reasoning. Directly inspired by Descartes, the Dutch
philosopher Baruch Spinoza was a similar rationalist in the 17th century with a religious
agenda in his Judaism, an aspect permeating most of his theory. Instead of stating that there
are two distinct substances composing existence, like Descartes, he proposed that everything
was a manifestation of the same substance, a divine substance he associated with the Jewish
god. It can be known without reference to anything outside of it, as we, our mind, nature, and
divinity, would merely be different aspects of the same substance. Concepts of free
will or probability would be meaningless, as everything happens necessarily as the divine
will directs. Good and evil also do not exist, and all we see are imperfections due to our limited
capacities as mere humans. His work was viewed as blasphemous from the perspective of Judaism,
and he was excommunicated from the religion, an act which remains in place to this day.
Another rationalist was Blaise Pascal, an important mathematician, and also a
physicist and writer in the 17th century who, much like Galileo Galilei, never wrote
anything specifically on philosophy. However, from his writings we can observe that he had
a very similar dualist position as his fellow countryman Descartes, though he denied both
rationalism and empiricism to focus on fideism, the idea that faith is more important than reason
to acquire knowledge. As his position suggests, he also thought theology and philosophy of
religion were of much greater importance than any other area of knowledge. His writings
were not of great relevance except for a few concepts in philosophy of mathematics, and the
well-known Pascal’s wager, an argument for the belief in the Christian god relying on statistics,
which we will briefly analyze in another tutorial. Finally, one of the last rationalists was the
German Gottfried Leibniz. A noteworthy scholar, he developed important material on several
areas of philosophy but also in physics, mathematics, jurisprudence, geology, and history,
besides several inventions. Akin to his fellow rationalists, and even the atomists millennia
before him, Leibniz envisioned that the fabric of existence was composed of several monads,
atom-like individual, indivisible, and immaterial substances which act in harmony with each other
in a “soul-like” manner according to their purpose or perception, designated by the Christian god.
Each of them are unique and eternal, and different kinds of monads would be present in different
contexts, and their relations could be understood with proper logical analysis and obeying a set of
principles which he frequently posited. These were the previously mentioned principle of Sufficient
Reason, and a few others like Aristotle’s non-contradiction principle, in which a statement
cannot be true and false at the same time. This strong metaphysical conception of the
world was a direct development of Descartes while attempting to bridge the mind-body divide
– a proto-idealistic perspective – however still regarding the physical world as mere appearances
from different settings of monads. In the realm of ethics, he tried to argue about the
problem of the existence of evil in the world, appealing to the fact that if God exists,
and if he is good, the existence of evil can only be explained if this world is the best
of possible worlds. This is a relatively flawed argument also known as “Leibnizian optimism”,
motivated by his religious belief. At any rate, today there is an entire field of logic that
studies the realm of possibilities based on this analogy with possible worlds, called modal logic.
Rationalist philosophy greatly influenced the posterior idealist thinkers, as both their
naming and ideas are clearly more inclined toward rationalism than to empiricism, even though
they claim to conceive of a balance of the two. In the next tutorial, we’ll take a look at
these empiricists to understand how they viewed the world in an almost completely
different fashion than the rationalists.
