Logic Theorist facts for kids

Logic Theorist was a special computer program created in 1956. It was made by three smart people: Allen Newell, Herbert A. Simon, and Cliff Shaw. This program was the very first one designed to do "thinking" or "reasoning" on its own, like a human. Because of this, many people call it the first artificial intelligence (AI) program.

Logic Theorist was able to prove 38 out of 52 math problems (called theorems) from a famous book called Principia Mathematica. It even found new, shorter ways to solve some of these problems!

How It All Started

When Allen Newell and Herbert Simon began working on Logic Theorist in 1955, the idea of "artificial intelligence" didn't even exist yet. The term "artificial intelligence" was actually made up the next year.

Herbert Simon was a political scientist. He studied how large organizations work and how people make decisions. He believed that understanding how businesses run was similar to understanding how humans solve problems and make choices. Simon once saw a computer printing a map using regular letters and symbols. This made him think that a machine that could move symbols around could also make decisions, maybe even think like a human!

The program that printed the map was written by Allen Newell. He was a scientist who studied how things are organized. For Newell, a big moment happened in 1954. Another scientist, Oliver Selfridge, showed his work on "pattern matching." Newell suddenly realized that simple computer steps could lead to very complex actions, even intelligent ones. He later said, "It all happened in one afternoon." It was a moment of great discovery for him.

Newell and Simon started talking about teaching machines to think. Their first big idea was a program that could prove math theorems. They wanted it to solve problems like those in the Principia Mathematica book by Bertrand Russell and Alfred North Whitehead. They asked Cliff Shaw, a computer programmer, to help them build the program. Newell said Cliff was the "real computer scientist" of the group.

The First Test

The very first version of Logic Theorist wasn't run on a computer. Instead, they "simulated" it by hand! In January 1956, Simon gathered his wife, three children, and some students. Each person was given a small card with a part of the program written on it. So, each person became a "component" of the computer program. They showed that the program could solve math problems just as well as a skilled mathematician. Later, Cliff Shaw was able to get the program running on a real computer.

A Cool Reception

In the summer of 1956, some important computer scientists held a conference. They called it the "artificial intelligence" conference. Newell and Simon proudly showed off Logic Theorist. But people didn't seem very impressed. Pamela McCorduck, who wrote about this, said that "nobody except Newell and Simon themselves understood how important what they were doing was." Simon later said they were "probably fairly arrogant" about it. He felt that the other scientists didn't want to hear from them, even though they had already created the first example of what everyone was talking about.

Logic Theorist quickly proved 38 theorems from the Principia Mathematica. One of its proofs was even better than the one Russell and Whitehead had worked so hard to create by hand. Simon showed this new proof to Russell, who was "delighted." They tried to publish the new proof in a math journal, but it was rejected. The journal said a new proof for a simple math problem wasn't important enough. They seemed to miss the amazing fact that a computer program had created it!

Newell and Simon continued to work together for many years. They started one of the first AI labs and created other important AI programs and ideas.

How Logic Theorist Worked

Logic Theorist was a program that performed logical steps on logical ideas. Think of it like this:

What It Understood

• An "expression" was a logical idea, like "If it rains, then the ground is wet."
• The program had two types of memory: "working" and "storage."
• Working memory held small parts of an idea.
• Storage memory held all the known facts and proven math rules.
• Each expression was like a tree, where each part of the idea was a "node" with details about it. For example, in "not P implies (Q and not P)," the "implies" part would be the main idea, pointing to "not P" and "Q and not P" as its branches.

How It "Thought"

The program used different levels of "processes" to solve problems:

• Instructions: These were the simplest steps, like "take the right part of this idea and put it here."
• Elementary Processes: These were groups of instructions that did a specific small task.
• Methods: These were bigger strategies made of elementary processes. There were four main methods:
  • Substitution: This method tried to change a problem into a known math rule by swapping out parts of it.
  • Detachment: If the program had an idea like "A leads to B," and it wanted to prove "B," it would look for a known rule like "Something leads to B." If it found one, it would then try to prove the "Something" part.
  • Chaining Forward: If the program wanted to prove "A leads to C," it would look for a known rule like "A leads to B." Then it would try to prove "B leads to C."
  • Chaining Backward: If the program wanted to prove "A leads to C," it would look for a known rule like "B leads to C." Then it would try to prove "A leads to B."
• Executive Control Method: This was the main boss method. It decided which of the four methods to try and in what order to solve each problem.

Logic Theorist's Big Impact on AI

Logic Theorist introduced several key ideas that became super important in AI research:

• Reasoning as Search: Logic Theorist solved problems by exploring a "search tree." Imagine a tree where the starting point is the problem you want to solve. Each branch is a step you can take using logic rules. Somewhere in the tree is the answer you're looking for. The path you take to get to the answer is the "proof." This idea of searching for solutions is still central to AI today.

• Heuristics: Newell and Simon quickly realized that the "search tree" could get huge very fast. They needed ways to "trim" the branches, meaning they needed "rules of thumb" to decide which paths were most likely to lead to a solution. They called these special rules "heuristics." This idea of using smart shortcuts to solve problems became a huge part of AI. It helps computers deal with problems that have too many possible solutions to check every single one.

• List Processing: To make Logic Theorist work on a computer, the three researchers created a special programming language called IPL. This language used a way of organizing information called "list processing." This same idea later became the basis for another important AI programming language called Lisp, which AI researchers still use.

What Logic Theorist Made People Think About

Pamela McCorduck wrote that Logic Theorist was "proof that a machine could do tasks that were thought to be intelligent, creative, and only for humans." It was a huge step in understanding artificial intelligence and what intelligence itself means.

Herbert Simon once told his students in 1956, "Over Christmas, Al Newell and I invented a thinking machine." He also wrote that they "invented a computer program capable of thinking non-numerically, and thereby solved the venerable mind-body problem, explaining how a system composed of matter can have the properties of mind."

This idea, that machines could have minds just like people, was later called "Strong AI" by a philosopher named John Searle. It's still a big topic of discussion today!

Pamela McCorduck also saw Logic Theorist as the start of a new way to understand the mind. This was called the "information processing model." She wrote that this idea became as important to understanding the mind in the 20th century as Darwin's idea of natural selection was to understanding biology in the 1800s. Newell and Simon later made this idea more formal, calling it the "physical symbol systems hypothesis."