2In this study, we start by proposing a causal induction model that incorporates symmetry bias. This 3 model is important in two aspects. First, it can reproduce causal induction of human judgment with higher 4 accuracy than conventional models. Second, it allows us to estimate the level of symmetry bias of subjects 5 from experimental data. We further propose an inference method that incorporates the aforementioned causal 6 induction model into Bayesian inference. In this method, the component of Bayesian inference, which 7 updates the degree of confidence for each hypothesis, and the component of inverse Bayesian inference that 8 modifies the model of the hypothesis coexist. Our study demonstrates that inverse Bayesian inference enables 9 us to deal flexibly with unstable situations where the object of inference changes from time to time. 10 11 Author summary 12 We acquire knowledge through learning and make various inferences based on such knowledge and 13 observational data (evidence). If the evidence is insufficient, then the certainty of the conclusion will decline. 14 Moreover, even if the evidence is sufficient, the conclusion may be wrong if the knowledge is incomplete in 15 the first place. In order to model such inference based on incomplete knowledge, we proposed an inference 16 system that performs learning and inference simultaneously and seamlessly. Prepare two coins A and B with 17 different probabilities of landing heads, and repeat the coin toss using either of them. However, the coin that 18 is being tossed is also replaced repeatedly. The system observes only the result of coin toss each time, and 19 estimates the probability of landing heads of coin tossed at the moment. In this task, it is necessary not only 20 to estimate the probabilities of the landing heads of coin A and B, but also to estimate which coin is being 21 used at the moment. In this paper, we show that the proposed system handles such tasks very efficiently by 22 simultaneously performing inference and learning. 23 24 25As a cognitive bias observed in humans, the disposition to infer from 'if P then Q' to 'if Q then P' 26 or to 'if not P, then not Q' is well documented [1, 2, 3, 4, 5, 6, 7, 8]. The former is termed symmetry bias [9] 27 and the latter is termed mutual exclusivity bias [4]. 28 Consider a simple example. We tend to infer from 'if you clean the room, then I will take you out' 29 to 'I will take you out if and only if you clean the room' or 'if you don't clean the room, then I will not take 30 you out'. Although these inferences are invalid according to classical logic, various people are inclined to 31 make them regardless of age. 32 In contrast, among non-human animals, the symmetry bias has been reported in behaviour of only 33 some California sea lions [10] and chimpanzees [11]. Although the symmetry bias produces wrong inferences 34 from the classical logic point of view, humans do show some positive features apparently stemming from the 35 symmetry bias. For instance, once you are able to respond to th...