It is shown that the instability of a liquid jet in relation to an external electric field and its instability in relation to the presence of an external material medium at the existence of common phenomenological features differ by threshold values of the field parameter and the Weber parameter, at which a specified instability is realized for the first two values of the azimuthal mode. For the next, a bending-deformation mode in the ascending order of number, both instabilities have thresholds that differ only in the values of the wave numbers at which they are realized. For the mixed electric-aerodynamic instability, when both the and the Weber parameters are different from zero, both the instability implementation thresholds and critical wave number change.