What Is Intelligence, Really?
Everyone uses the word intelligence, and almost no one defines it the same way. So we will not start with a definition. We will start with a loop.
An agent is anything that takes in a situation and produces an action. An environment is everything the action lands on. The environment answers with a new observation and a reward — a number saying how well that went. Intelligence, for our purposes, is whatever lets the agent choose actions that raise the reward over time.
That is deliberately modest. It covers a thermostat, a chess engine, a foraging ant, and a large language model. It does not require consciousness, feelings, or a soul.
Three words, one loop
The loop is the whole field in miniature. Almost every idea later in this guide is an answer to one of three questions: how does the agent represent the world, how does it choose, and how does it learn from what came back?
Three levels people confuse
Most arguments about AI are people talking at different levels. Keep them apart.
The one sentence to keep
Intelligence is the ability to take useful action under uncertainty.
Everything else in this guide is machinery for that sentence. We begin where the uncertainty lives: in information itself.