Rule-based learning is an important aspect of language acquisition. Yang (2005,2016) proposed the Tolerance Principle (TP) to predict when a rule will be formed by the language learner. We present the derivation of the TP as originally proposed and test it on both hypothetical data and corpus data from 8 children. Results for the hypothetical data contradict the TP’s predictions, as do the data from 7 of the 8 children. We conclude that the original form of the TP does not explain rule-learning.