Gersonides facts for kids

Levi ben Gershon (1288 – 20 April 1344), also known as Gersonides, was a very smart Jewish scholar from medieval France. He was a philosopher, a mathematician, a physician, and an astronomer. People also called him Ralbag, which is a short Hebrew name for him. He was born in Bagnols-sur-Cèze, France.

About Gersonides

Not much is known about Gersonides' daily life. His family was known for being very religious and good at understanding Jewish texts. Even though he wrote important comments on parts of the Bible, he never became a rabbi. Some people think his unique ideas might have stopped him from getting a higher position. He lived in cities like Avignon and Orange. He is thought to have died in 1344.

Gersonides had some very new ideas for his time. He was a big follower of the Greek thinker Aristotle. This led him to explain some Bible miracles in a more natural way. Other important scholars did not always agree with his writings. They sometimes criticized his views strongly.

His Main Book: The Wars of the Lord

Gersonides' most important book is called Sefer Milhamot Ha-Shem, which means "The Wars of the Lord." He spent twelve years writing it, from 1317 to 1329. A part of this book, which talked a lot about astronomy, was even translated into Latin in 1342 for Pope Clement VI.

This book was inspired by another famous Jewish philosophy book, the Guide for the Perplexed by Maimonides. Gersonides' book looked closely at Maimonides' ideas. He wanted to make sure they fit well with Aristotle's thinking.

The Wars of the Lord covered many big topics:

• The Soul: He talked about how the soul works and how people gain knowledge.
• Prophecy: He explored how prophets receive messages from God.
• God's Knowledge: He had a special idea that God knows all possible choices, but not exactly which choice a person will make. This means people still have free will.
• Heavenly Bodies: He discussed the spiritual beings in the heavens and shared ideas about astrology.
• Creation and Miracles: He had different views from Maimonides on how the world was created and how miracles happen.

Gersonides also wrote comments on many books of the Bible. These included the Pentateuch, Joshua, Judges, Samuel, Kings, Proverbs, and Job.

Views on God's Knowledge

Gersonides believed that God knows all the choices available to people. However, he thought God does not know which specific choice a person will make. This idea was meant to explain how God's knowledge can exist alongside human free will. This means people are truly free to make their own decisions. Other Jewish thinkers also supported this idea.

Views on the Afterlife

Gersonides thought that people's souls have two parts. One part is the "material intellect," which helps us learn and understand. This part dies with the body. The other part is the "acquired intellect." This part survives after death. It holds all the knowledge a person gained during their life. So, for Gersonides, a person becomes immortal by gaining knowledge, especially in subjects like mathematics and natural sciences.

Talmudic Writings

Gersonides also wrote about Jewish law and traditions. He wrote a commentary on the thirteen rules of Rabbi Yishmael. Only one of his Talmudic works is still available today.

Works in Science and Math

Gersonides made many important discoveries in math and science. However, he wrote mostly in Hebrew. Because of this, his ideas did not spread widely to other parts of the world.

Mathematics

In 1321, Gersonides wrote a math book called Maaseh Hoshev. This book talked about how to do math problems. It included finding square and cube roots. It also showed early uses of mathematical induction. This is a way to prove that a statement is true for all numbers. He also did important work in combinatorics, which is about counting different ways things can be arranged.

In 1342, he wrote about trigonometry. He proved the sine law for triangles and created tables for sine values. A year later, he solved a problem about "harmonic numbers." These are numbers that are powers of 2 and 3. He showed there are only four pairs of these numbers that differ by 1.

Astronomy and Tools

Gersonides is believed to have invented the Jacob's staff. This was a tool used to measure the angle between stars or planets. It helped sailors and astronomers find their way and study the sky.

He observed a solar eclipse in 1337 and a lunar eclipse in 1335. He used a camera obscura to make observations of the Moon, Sun, and planets. He also had some ideas that were not correct, like believing the Milky Way was just reflected sunlight.

Stellar Distances and Ptolemy's Model

Gersonides was one of the first astronomers to realize that stars are much, much farther away than planets. Most astronomers at the time thought stars were just beyond the outer planets. Gersonides estimated the distance to stars to be incredibly vast.

He also challenged the popular model of the universe by Ptolemy. Ptolemy's model used circles within circles (epicycles) to explain how planets moved around Earth. Gersonides used his own observations to check this model. He looked at how the brightness of Mars changed. His observations did not match Ptolemy's model at all. This was a very early example of testing a scientific theory with observations. Although his findings did not directly lead to Copernicus's heliocentric model, Gersonides was the first to show that Ptolemy's ideas had problems.

The lunar crater Rabbi Levi is named after him.

Astrology

Gersonides believed in astrology, but he had a natural explanation for it. He thought that the positions of stars and planets influenced events on Earth. He believed that a person's birth constellation could affect their nature and future. However, he also thought that human free will could change the path set by the stars.

In Modern Stories

Gersonides is an important character in the novel The Dream of Scipio by Iain Pears. In the book, he teaches the main character, Olivier de Noyen. The story also includes a made-up meeting between Gersonides and Pope Clement VI.

Awards

• 1985: National Jewish Book Award Scholarship for The Wars of the Lord

See also

In Spanish: Gersónides para niños