We consider the problem of approximately verifying the truth of sentences of tuple relational calculus in a given relation M by considering only a random sample of M. We define two different measures for the error of a universal sentence in a relation. For a set of n universal sentences each with at most k universal quantifiers, we give upper and lower bounds for the sample sizes required for having a high probability that all the sentences with error at least ε can be detected as false by considering the sample. The sample sizes are O((log n)/ε) or O((|M|^1–1/k)log n/ε), depending on the error measure used. We also consider universal-existential sentences.