<p>The paper focuses on Janina Hosiasson’s psychology of inductive reasoning. Hosiasson similarly to Frank P. Ramsey supported the theory of partial beliefs, which argues that a person’s subjective belief in probability may be measured by his or her actions. The theory suggests that people aim to do as much good as possible, and their behaviour is influenced by this goal. At the same time, Hosiasson claimed that Ramsey’s theory holds only if the person behaves rationally, and she demonstrated in experiments with her students that this was not always the case. For instance, although the students possessed a certain amount of information, they were not able to follow the most rational strategy when more complex calculations were required. Forty years later, Amos Tversky and Daniel Kahneman proposed a theory of cognitive bias, pointing out the limits of rationality. Their finding confirmed Hosiasson’s results, as the present study shows.</p>