History of Logic

Origins of logic in the West

Precursors of ancient logic

There was a medieval tradition according to which the Greek philosopher Parmenides (5th century bce) invented logic while living on a rock in Egypt. The story is pure legend, but it does reflect the fact that Parmenides was the first philosopher to use an extended argument for his views rather than merely proposing a vision of reality. But using arguments is not the same as studying them, and Parmenides never systematically formulated or studied principles of argumentation in their own right. Indeed, there is no evidence that he was even aware of the implicit rules of inferenceused in presenting his doctrine.

Once people have seen that something happens through observation, sooner or later it will occur to them to ask why it happens, and whether there is any way of proving that it will happen the same way every time. The Egyptians, according to Herodotus, used experiments to see what would happen in a certain situation. For instance, he reports that the Pharaoh wanted to find out what the first language on earth was, and so he ordered two babies to be put in a house alone, and the slaves who took care of them should not speak at all, to see what they would say first.

In the classical period in Greece, Pythagoras was interested in proving that things were true all the time, rather than just observing that they were true most of the time. Socrates began to develop a way of thinking and speaking which would let you prove that a certain statement was or was not true, which we call logic. Socrates' student Plato continued this idea, and Plato's student Aristotle began the process of applying this logic to the natural world.

In the Hellenistic period, many Greek philosopher-scientists like Euclid and Aristarchus used Aristotle's logical system to investigate mathematics, biology, physics, astronomy, and medicine. These studies took place all over Alexander's empire, but especially in the great Library at Alexandria inEgypt.

When the Romans took over Greece and Egypt, they became great admirers of the Greek scientific process. The Library at Alexandria remained open. But really not as many great advances in understanding the natural world were made during the Roman Empire. The Romans were more interested in practical engineering, and more people studied that. With theconversion to Christianity in the 300s AD, there got to be a lot of hostility to the Library, which was seen as a stronghold of paganism, and eventually, around 600 AD, the Library was shut down.

After the Islamic Empire was established in the late 600s AD, scientific research took off again. In physics, Ibn Sina figured out the basic natural laws governing motion andmomentum in the 900s AD. In the 1100s AD, Maimonides realized that people got sick from bad water and air (though he didn't know about germs), rather than from magic spells or curses. Ibn Rushd, at the same time, tried to use logic to figure out the nature of the soul.

During this time in Europe, little or no scientific progress was being made. People in Europe could barely read or write. But by the 1100s AD, Europe was for the first time becoming a center for scientific thought. Monks, in the role of professors, were teaching Socratic logic to students in the monastic schools and cathedral schools (the beginnings of modern universities) at Paris and Cambridge and Oxford. Men like Peter Abelard tried to use logic to prove the existence of God, and to define His nature. At the ducal court of Aquitaine, Eleanor of Aquitaine and her court used the same logical principles to discuss the nature of love.

By the 1200s, there were increasing connections between Islamic and European scholars. Thomas Aquinas imitated the work of Maimonides, Ibn Sina and Ibn Rushd to build a more logical version of Christianity. In the next century - the 1300s AD - Ibn Khaldun in North Africa applied logical principles to the study of history and economics, breaking new ground.

Observation

Before people had any idea why anything happened, or how, they could at least find out what happened. People watched plants grow, they watched animals grow, they watched the sun go up and the stars and planets go around, and the seasons change, and they figured out a great many things about what happened. In fact, people of theStone Age probably knew more about what happens in nature than you do, because that was more important for them than it is for you.

We often think today that people who lived a long time ago did not understand what makes plants grow, or where babies come from. But this is really not true. Anthropologists have never found any people on earth who didn't know both of those things very well. Anybody who looks around her will see that plants grow whereseeds or spores fall on the ground, and that babies come from a mother and a father.

Constellation of Orion; thanks to Douglas Cooper

Another form of observation was the development of counting. As far back as the Paleolithic (Old Stone Age), about 35,000 years BC, people were carving marks on sticks to help them remember how many bags of fruitwere in that basket or how many people were in the band. TheSumerians, about 4000 BC, were probably the first people to develop a way of writing numbers down more efficiently.

The Egyptians and the Babylonians were both very accurate and interested observers of natural phenomena. They identified and named the different constellations of stars. They also observed less obvious things, like the Pythagorean Theorem.

The Greek philosopher Aristotle brought the Greek interest in bringing order to the natural world to scientific observation, in the 300s BC. He tried to organize all of nature into a system that made sense, putting similar things together into categories. Aristotle got his friend Alexander the Great to send him back samples of new plants and animals that he found on his military campaigns, from as far away as India.

Not long after Aristotle came another Greek observer, a doctor named Hippocrates. Hippocrates made many observations about sick people, and he and his students wrote down what they observed, and their ideas about what it meant.

Under the Romans, Pliny the Elder around 70 AD collected masses of information into his Natural History, though mostly in order to show how big and powerful the Roman Empire was, that it had all these things in it. Pliny didn't really care what it meant.

A Roman doctor named Galen also added a great deal to Hippocrates' observations.

After the rise of Christianity, there was not much scientific observation going on in Europe for a while. In the Islamic Empire, from 700 AD on, on the other hand, people were very interested in scientific observation. Some people were interested in plants, and copied the Roman works while adding any new information they could find. Others, like Ibn Riza and Maimonides, were doctors, and added a lot of new observations (and also treatments) to those of Galen.

Logic of the Scientific Method

Where Does God Fit In?

Gods are part of people's desire to know how the world works. One of the ways that people explain how the world works, is to say that God or the gods make this happen. Or you could say that the gods are a way of talking about things that happen, that are hard to understand or hard to talk about.

So the Sumerians said that there was a sky god, Ur, who controlled the weather, and a fertility goddess, Ishtar, who controlled whether things grew or not. And theEgyptians said that there was a god, Thoth, who decided what happened to you after you died. And the Jews said that God had created the world. And the Germans said that the gods made thunder. And the Greeks said that gods could predict the future.

In the ancient and medieval worlds, nobody, not even scientists, seems to have seriously thought that there might not be any gods. Everybody believed in at least one god. Everyone believed that the discoveries people made through observation and the logical systems they thought of could work with the idea of gods. People disagreed about which gods, and about what exactly the gods wanted, but nobody questioned that there were gods.

Because of their faith, people were not afraid to apply their observations and their reasoning to thinking about the gods. They used logic and observation to try to find out who the gods were and what they wanted. The Sumerians observed the stars, and organized them into the twelve signs of the Zodiac. The Greek Plato wrote about the nature of the soul, and how you could figure it out logically. The Roman Lucretius wrote a long, logically constructed book about how the gods acted toward people, and why, which also includes a lot about the theory of atoms. Around 420 AD, the great Christian writer Augustine also used Aristotelian logic to work out what God's plan was, and why God had allowed the Visigoths to sack Rome.

With the rise of the new religion of Islam in the 600s AD, many scientists living in the Islamic Empire also tried to work out the relationship between Aristotle's science and theQuran. About 1050 AD, Al Ghazali supported a clear division between mathematical and astronomical ideas, which you could prove, and religious ideas, which were in a different category. Ibn Rushd, about 1150 AD, wrote a book in opposition to Al Ghazali, explaining how Aristotle's ideas could work with the Quran after all. A little bit later, about 1175 AD, the Jewish doctor Maimonides wrote a book explaining how Aristotle's ideas could work with the Jewish Torah. In Europe, in the 1200s AD, the Christian churchman Thomas Aquinas built on all this work to explain how Aristotle's ideas could work with the Christian Bible.