This thesis. Propositions. 1. Problem Before one can stand on the shoulders of giants, one first has to climb them. 2. Rationality Assumptions about processes of scientific discovery imply assumptions about psy- chological processes, and vice versa. 3. Neuropharmacology A part of reasoning in neuropharmacology can be modeled as reasoning about quali- tative differential equations, and can be assisted by a computer. 4. Logic Reasoning in scientific discovery includes logical fallacies, which are necessary to introduce new hypotheses by abduction. 5. Cognition To understand the rationality of (secondary) cognitive processes of symbolic problem solving in science, one also needs to understand how these processes are controlled by (primary) cognitive processes of probabilistic learning. 6. Computation One has learned something when one can compute part of the same output with less input. 7. Theory Rationality in discovery, in theory, includes inferring hypotheses that best explain observations, and inferring predictions that can experimentally test those hypotheses best. 8. Practice Rationality in discovery, in practice, also includes inferring the best interventions in designing drugs, treatments, and experimental conditions to explore phenomena. 9. Discovery Interdisciplinary scientists build bridges that other scientists are not eager to cross.