An avian analogue to humanartificial orsynthetic grammar learning (Reber, 1967) was developed. Pigeons viewed horizontal strings of three to eight colored letters. These strings either conformed to Reber’s artificial grammar or violated it in one or two locations. Pigeons categorized the letter strings asgrammatical (left keypeck) ornongrammatical (right keypeck). Overall accuracy of categorization was above chance to both familiar training strings and to novel transfer strings, thereby satisfying a conventional criterion for learning anabstract concept. The results support amultiple mechanisms point of view according to which pigeons, like humans, learn both abstract concepts and specific strings, or specific parts of strings, in artificial grammar learning tasks.