Aristotle may have been a genius when it came to philosophy — especially logic — but he didn't know squat about science. Sure, we can't excel in every field we try our hand in, but Aristotle's massive errors aren't just a personal embarrassment to him — they directly hampered scientific progress for 1,800 to 2,000 years.
The problem is that from the time he was alive (the fourth century BC) until the Enlightenment, when Aristotle said something, that was the end of the argument. Isaac Asimov notes, perhaps with a tinge of jealousy: “No matter who disagreed with them, even other philosophers, Aristotle's ideas — whether right or wrong — usually won out.” Chemist John Appeldoorn writes that “Aristotle's teachings were unquestioned. After eighteen centuries, universities accepted them as if they had been written in stone.”
For example, Aristotle didn't believe that plants were divided into male and female sexes, so there the matter stood for two millennia, until botanists stated the obvious in the 1700s.
He was also wrong about inertia, and again the world had to wait — this time for Galileo, followed by Newton — to speak the truth that objects in motion stay in motion, while objects at rest stay at rest, unless acted upon by outside forces.
Like most Greeks, Aristotle championed the view that the Sun and planets revolved around the Earth. Copernicus (in the early 1500s) and Galileo (100 years later) had to risk their reputations and their lives to put the kibosh on that nonsense.
He further surmised that outer space was made up of 54 spheres and that there were only seven heavenly bodies, which were fixed and unchanging. This meant, for one thing, that comets had to be in Earth's atmosphere. Only in 1577 was this notion put out to pasture. Over the next 50 years, belief in the heavenly spheres faded.
Aristotle declared that heavier objects fall faster than lighter ones, an error that could've been exposed with simple experiments. It wasn't until 1,900 years later that Galileo dropped objects off the Tower of Pisa, proving that all things obey gravity at the same rate. By that time, Galileo already had been kicked out of the University of Pisa for daring to question Aristotle's theory.
Some Greeks, including Democritus and Hippocrates, surmised that the brain was the seat of thought, intelligence, and emotion. Tish-tosh, said Aristotle, it's the heart — and that became the accepted wisdom. Aristotle wrote: “The brain is an organ of minor importance, perhaps necessary to cool the blood.” Because Greek physicians primarily held brain-centered views, that remained a strong undercurrent, yet Aristotle's heart view dominated until the 1500s.
A fellow Greek philosopher, Democritus, postulated that the physical world was made up of tiny pieces of matter, which he called atoms. But Aristotle pooh-poohed this ridiculous notion, causing it to languish in obscurity until the second half of the 1600s, when scientists began to resurrect it. It wasn't until the first years of the 1800s that the existence of atoms was universally accepted.
Who knows how much further science would've progressed if Aristotle had stuck to syllogisms? 