The first half of Part 2 of Descartes’ Discourse ends with his warning that two sorts of people
should not attempt his new method. Men of hasty judgment would succeed in doubting
their received opinions, but without the mental self-discipline to follow through on the method,
they would “remain lost all their lives.” And people who know they lack the mental
ability to reliably distinguish true from false should put this book down and trust
in the truths they receive from wiser minds. Notice two things Descartes implies about the
reader here, perhaps as flattery: the reader must have the self-discipline and mental acuity needed
to complete the reform process once begun. Anyone with doubts about his possession of
either of these abilities would be better off as he is, and should not follow Descartes’ path.
Assuming we think ourselves up to the challenge, we press forward into the second half of Part 2,
starting at margin note 16. Descartes tells us
he would himself have been in this second group, trusting in the wise instruction of his teachers,
if he had not had so many teachers, giving such contradictory advice. He cites two sources for his
incredulity toward what he was taught: first, there is no opinion so crazy or incredible
that it has not been defended by some philosopher or other. Rather than being
the storehouse of reason, philosophy is full of wild and contradictory views.
Second, in his travels across Europe after leaving school, Descartes saw the diverse
and incompatible customs and beliefs of people in different cultures. Yet he also saw that
these people were not irrational or insane, but used the same reason as everyone else.
At the end of this paragraph he draws two conclusions from these experiences:
first, “we are clearly persuaded more by custom and example than by any
certain knowledge” in matters of how to live. Second: Popularity of an opinion is no proof
of its truth; in fact it seems more likely that a single person would have found the truth,
rather than a whole nation of people. Note that this is a very Platonic/Socratic point:
the mob is foolish but only the few are wise. Thus, reasons Descartes,
he could not find reasons to accept any one received opinion over any other, and he was
left to figure out the truth on his own. How should he proceed? His guiding principle
will be caution, he tells us. He resolves to advance very slowly, so that even if he covers
little ground, at least he avoids error and his gains are secure. He compares himself to
a man walking alone in shadow, and if you have ever navigated your home at night, you know the
carefulness Descartes describes here: there’s no rush, just be careful not to put a foot wrong.
He needs a plan for systematically evaluating all his knowledge, so this is what he turns to next.
In his education, three fields stand out as possibly helpful in this project: logic,
geometrical analysis, and algebra. Each of these has its strengths and flaws.
What Descartes wants is a method combining the virtues of all three,
without any of their defects. Let’s look at those virtues and defects now.
Logic certainly gives us a method of obtaining certainty, reasoning forward from given premises.
But it can only draw out the implications of what we already know, and it can be misused
by rhetoricians. Furthermore, if any of the starting premises is false, the conclusion
is not certain. And, Descartes tells us sadly, false premises are common among philosophers.
Analysis and algebra are clear and give certain results. But they deal
with abstractions that are not useful for daily life. Analysis focuses on numbers
rather than actions and things, and algebra is imprisoned by its many rules and symbols.
So Descartes’ new method will attempt to combine the strengths of these three fields,
while avoiding their limitations.
To keep matters simple he has just four rules, which he resolves never to break, not even once.
Rule 1. Do not accept as true anything I do not clearly know to be true. In other words,
accept only what is clearly and distinctly present to my mind in each judgment I make.
Rule 2. Divide up each problem into as many pieces as needed in order to solve it easily.
In other words, analyze and subdivide difficult problems into simpler ones, until each unit
is small enough to grasp clearly and distinctly. Rule 3. Keep my thoughts orderly by beginning
with what is simplest and easiest to know, then building up gradually to what is complex
and difficult. And (this is important) work by assuming there is an order to things,
even when I cannot perceive any order in them. Rule 4. Be complete in my calculations and
thorough in my reviews, so I am sure I leave nothing out. In other words,
maintain self-discipline throughout the whole process of knowledge discovery and checking.
Before we go on, let me make a few comments about these rules.
Rule 1 sets a very high standard for accepting anything as true. It suggests that I will find
a large number of my current beliefs fail this test, and I cannot yet accept them as true.
Rules 2 and 3 give me a way of building back my beliefs, though. Rule 2 tells me to analyze,
break up into smaller parts. Is my belief B clearly true? No? Then break it up into smaller
parts. Are each of the parts clearly true? No? Then break them in to smaller parts too.
Repeat this until I arrive at a belief that is so simple,
clear, and distinct, that its truth is clearly impressed on my mind.
Then, by Rule 3, build up from these small clear true beliefs,
back to more complex beliefs about myself and the world, always following the right order.
Rule 4 reminds me to maintain the mental self-discipline
and follow-through necessary to complete this process and not become lost forever.
Descartes then compares his task to the long chains of reasoning used in geometry and logic
to prove a difficult truth by many small steps. His hope is that all possible human knowledge
will eventually follow from this simple but careful process of building up from clear truths.
Descartes tells us he began by applying his new 4-rule method to mathematics,
and that he achieved the solution of several difficult problems in just a few months.
But what he found even more pleasing than these solutions was the realization that
by his method he was now using his mind as well as it could be used in finding truth.
He had found the method best suited to using a human mind to discover truth.
As his mind became more accustomed to reasoning in this way, he began to hope that he could use the
method to find truths in areas of study outside mathematics. And here at the end of Part 2,
he sets his sights on philosophy, which provides the principles
of other sciences. Since he was (in the story he is telling us in the Discourse) only 23 years old
at the time, he resolved to do two things: to strengthen his mind by practicing the method,
and to travel and gather experiences that will be useful to him later on.
That brings us to the end of Part 2 of the Discourse on Method.
I hope you found this walkthrough helpful. Thanks for watching today; goodbye.