In the sensorimotor stage (0–2 years), intelligence takes the form of motor actions. Intelligence in the preoperation stage (3–7 years) is intuitive in nature. Thinking in the concrete operational stage (8–11 years) is logical but depends on concrete referents. In the formal operations stage (12–15 years), thinking involves abstractions. Piaget believed that it is this ability for abstract symbolic reasoning that distinguishes human beings from other animals.