In mathematics, a measurablecardinal is a certain kind of large cardinal number.
A real valued measurablecardinal not greater than c exists iff there is a countably additive extension of the Lebesgue measure to all sets of real numbers.
Although it follows from ZFC that every measurablecardinal is inaccessible (and is ineffable, Ramsey, etc.), it is consistent with ZF that a measurablecardinal can be a successor.