The basic concepts of probability theory include:

1. Sample space: It is the set of all possible outcomes of an experiment.

2. Event: It is a subset of the sample space.

3. Probability: It is a measure of the likelihood of an event occurring. It is a number between 0 and 1, where 0 represents impossible and 1 represents certain.

4. Addition rule: It states that the probability of the union of two events is equal to the sum of their individual probabilities minus the probability of their intersection.

5. Multiplication rule: It states that the probability of the intersection of two events is equal to the product of their individual probabilities if they are independent.

6. Conditional probability: It is the probability of an event given that another event has occurred.

7. Bayes' theorem: It is a formula that relates the conditional probability of an event with its inverse conditional probability.