Expert Systems also use heuristics in their problem solving. Heuristics are just rules of thumb that people follow in their problem solving, such as "If the sky is dark and you're going outdoors, then bring an umbrella along (in case it rains)".

Heuristics help to simplify the problem solving process greatly by limiting the search for solutions, but can only guarantee acceptable solutions. However, they are very appropriate for expert systems, as they often have to solve complex real-world problems that are difficult and frequently not very well understood and would simply be impossible or impractical to solve by algorithmic methods.