The tests leading to the determination of the strength of brittle materials show a very wide scattering and a noticeable difference between flexural and tensile strengths. The corresponding statistics are usually described by the Weibull law, which only partly explained the observed difference. From a theoretical point of view, the coupled criterion reaches the same conclusion, the flexural strength is higher than the tensile one. It is shown that these two approaches complement to give a satisfying explanation of the difference between the flexural and tensile strengths. Moreover, according to the coupled criterion, the tensile strength appears to be the only material parameter.