Consider two statements. First: "All bachelors are unmarried men." Second: "The sun is a star."

Both are true, but they are true in very different ways. To know the first statement is true, you don't need to conduct a survey of bachelors. You just need to understand the definition of the word "bachelor." The truth is baked into the language itself.

To know the second statement is true, however, understanding the words "sun" and "star" isn't enough. You need information about the world, gathered through observation and science. This fundamental difference splits propositions into two categories: analytic and synthetic.

Analytic statements are true by definition. They are essentially tautologies, where the predicate (the part of the sentence that modifies the subject) is already contained within the subject's definition. Think of them as unpacking a concept. If you know what a triangle is, you automatically know it has three angles. No further investigation is needed. The truth is confirmed by a dictionary, not by a telescope or a microscope.

Synthetic statements, on the other hand, synthesize or combine different concepts to tell us something new about the world. The concept "is on my desk" is not part of the definition of "my coffee cup." To know if the statement "My coffee cup is on my desk" is true, you have to look. The vast majority of statements we make in daily life and in science are synthetic. They are claims about the state of reality, and they can be proven true or false by experience.

While the ideas behind this distinction are old, the German philosopher Immanuel Kant formalized them in the 18th century. However, it was a group of philosophers and scientists in the early 20th century known as the logical positivists who made this distinction the cornerstone of their philosophy. They were fiercely empirical and wanted to clean up philosophy, which they felt was full of meaningless, unverifiable claims.

For the logical positivists, the analytic-synthetic distinction was a powerful tool. It gave them a way to sort statements into neat piles.

If a statement was analytic, it was true by definition and therefore meaningful. Mathematical truths like $2+2=4$ fell into this category. They were certain, but they didn't describe reality.

If a statement was synthetic, it was meaningful only if it could be verified through experience. Scientific claims like "Force equals mass times acceleration" belonged here.

Any statement that was neither analytic nor empirically verifiable was, in their view, philosophically meaningless. This included vast swaths of metaphysics and ethics. For them, a statement like "Stealing is wrong" couldn't be proven true by definition or by experiment, so it was relegated to the realm of emotion or opinion, not fact.

By using this distinction, the positivists aimed to establish a clear criterion for what could be considered knowledge. Only statements of logic and mathematics (analytic truths) and empirically verifiable claims of science (synthetic truths) made the cut. This created a tidy, logical picture of knowledge, firmly grounded in either pure reason or concrete experience. It was a foundational idea for understanding how language and science work, before later philosophers began to question how sharp this dividing line really is.