Near the end of Alexander's life, he began to suspect plots, and threatened Aristotle in letters. Aristotle was vocal about his dislike for Alexander's claim of divinity, and the king executed Aristotle's grandnephew Callisthenes as a traitor. Alexander died in Babylon in 323 without ever having returned to his native land. Upon Alexander's death, anti-Macedonian sentiment in Athens once again flared up, and Aristotle fled the city. However, he died in Euboea of natural causes that same year, 322 .
The three greatest ancient Greek philosophers were Aristotle, Plato, and Socrates. Socrates taught Plato, then Plato taught Aristotle. These three thinkers turned early Greek philosophy into the beginnings of Western philosophy as it is today. Aristotle taught Alexander the Great, who later conquered the entire Middle East.
Plato's main ideas were that knowledge from the senses was always confused and not pure. True knowledge can be gotten from the thinking soul that turns away from the world. Only the soul can have knowledge of "Forms", the real way things are. The world is only a copy of these "Forms" and is not perfect.
Aristotle thought differently. He thought that knowledge from the senses was more important. These thoughts became some of the roots of the scientific method after hundreds of years. Most of the things Aristotle wrote that we still have today are notes from his speaking and teaching. Some of his important writings are "Physics", "Metaphysics", "(Nicomachean) Ethics", "Politics", "De Anima (On the Soul)", and "Poetics".
He also had problems with the atomic theory. He did not believe in Democritus' theories about the atomic theory. He believed that all matter was continuous whereas Democritus stated the all matter was made up of tiny indivisible things called "atoms". Democritus was proved right by physicist John Dalton in 1804.
Aristotle created a form of logic. His logic is called "sentential logic" because it uses sentences for the syllogism.
Aristotle's logic influenced the history of Western thought. It was Aristotle's logic which was copied and used in the Arabic and Latin mediaeval traditions. It was dominant for two and a half thousand years, until the late 19th century. Then modern logic was started by Gottlob Frege, Charles Sanders Peirce and others.
Aristotle is the earliest natural historian whose work has survived in some detail. He certainly did research on the natural history of Lesbos, and the surrounding seas and neighbouring areas. The works "History of Animals", "Generation of Animals" and "Parts of Animals" have observations and interpretations, along with some myths and mistakes.
The most striking passages are about the sea-life round Lesbos. As well as live observation, he got specimens from the catches of fishermen. His observations on catfish, electric fish ("Torpedo") and angler-fish are detailed. His writing on cephalopods such as "Octopus", "Sepia" (cuttlefish) and the paper nautilus ("Argonauta argo") are accurate. His description of the hectocotyl arm, used in sexual reproduction, was widely disbelieved until its rediscovery in the 19th century. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (Selachimorpha).
Another good example of his methods comes from the "Generation of Animals" in which Aristotle describes breaking open fertilized chicken eggs at intervals to observe when visible organs were generated.
He gave accurate descriptions of ruminants' four-chambered fore-stomachs, and of the ovoviviparous egg development of the houndshark "Mustelus mustelus".
The works are traditionally listed in this sequence:
Aristotle is still one of the most influential people who ever lived. He contributed to almost every kind of knowledge in his day, and he started many new fields.
Aristotle was the founder of formal logic, pioneered the study of zoology, and helped to develop scientific method.
Despite these achievements, Aristotle's errors are thought by some, such as Peter Medawar, to have held back science considerably. Bertrand Russell notes that "almost every serious intellectual advance has had to begin with an attack on some Aristotelian doctrine". Russell also refers to Aristotle's "Ethics" as "repulsive", and calls his logic "as definitely antiquated as Ptolemaic astronomy". Russell says these errors make it difficult to do historical justice to Aristotle, until one remembers what an advance he made on his predecessors.
The immediate influence of Aristotle's work was felt as the Lyceum grew into the Peripatetic school of philosophers. Aristotle's influence over Alexander the Great is seen in the latter's bringing with him, on his expedition, biologists and researchers.
Carl Sagan
Carl Edward Sagan (November 9, 1934 - December 20, 1996) was an American astronomer. He was very interested in what life on other planets would be like, which is known as SETI (search for extraterrestrial intelligence).
Sagan was a science communicator, which meant he taught people about science. He felt like the general public was losing interest in science, so he wrote many books and appeared on television to make it popular again. He mostly talked about planetary science and topics related to space. One of his most famous works includes. "Cosmos: A Personal Voyage. Cosmos" was a television series about many different scientific topics, which Sagan co-wrote and narrated. It made him very famous outside the world of science.
Sagan supported the scientific method and scientific skepticism.
Carl Sagan was born in Brooklyn, New York City. Carl's family was Jewish. His father, Samuel Sagan, was an immigrant from the Russian Empire. Samuel was born in 1905 in a city called Kamianets-Podilskyi. The Russian Empire no longer exists, so today Kamianets-Podilskyi is in Ukraine. Samuel made clothes for a living. Carl's mother, Rachel Molly Gruber, was a housewife. Carl had a sister named Carol, who became a social worker. Carl was named after his grandmother, Chaiya (Clara).
Sagan attended the University of Chicago earning two degrees in physics. He followed with a doctorate in Astronomy in 1960 and taught at Harvard University until 1968, when he moved to Cornell University.
Sagan became a teacher and director at Cornell in 1971. He helped many unmanned spacecraft to explore outer space. He thought of the idea of putting a message on spacecraft which could be understood by any life from another planet that might find it. The first message sent into space was a large gold-plated label on the space probe Pioneer 10. He continued to make the messages better. The last message he helped with was the Voyager Golden Record that was sent out with the Voyager space probes.
He was well known as a writer who warned of the dangers of nuclear winter. He helped people learn about the atmosphere of Venus, seasonal changes on Mars, and Saturn's moon Titan. He showed that the atmosphere of Venus is very hot and dense. He also said that global warming was a growing, man-made danger like the natural development of Venus into a hot and dangerous planet with greenhouse gases. He suggested that the seasonal changes on Mars were due to dust storms.
Sagan was among the first to guess that Titan and Jupiter's moon Europa might have oceans or lakes, which means that life could be there. Europa's underground ocean was later confirmed by the spacecraft Galileo.
Sagan thought the search for life on other planets was a good idea. He said scientists should listen with large radio telescopes for signals from other planets. He thought sending probes to other planets was a good idea. Sagan was editor "Icarus" (a magazine about space exploration) for 12 years. He helped start the "Planetary Society" and was a member of the SETI Institute Board of Trustees.