the calculated interval has fixed endpoints, where μ might be in between (or not). thus this event has probability either 0 or 1. we "cannot" say: "with probability (1 − α), the parameter "μ" lies in the confidence interval." we only know that by repetition in 100(1 − α) % of the cases, μ will be in the calculated interval. in 100α % of the cases, however, it does not. and unfortunately we do not know in which of the cases this happens. that is why we say: "with confidence level 100(1 − α) %, "μ" lies in the confidence interval."