We have measured the ratio of the three-jet to two-jet inclusive cross section as a function of the total transverse energy of jets (H[sub T]=[summation]E[sup j][sub T]) in events in p[anti p] collisions at [radical]s=1.8 TeV. We find that for [summation]E[sub T]>200 GeV there is a 70% probability of emitting an additional jet with E[sub T>20 GeV. Using this measurement and the framework of the theory of Quantum Chromodynamics (QCD), we investigated the size of the renormalization scale used to model emission of ''soft'' (low-E[sub T]) jets in multijet final states. The findings indicate that, to order [alpha][sub s][sup 3] in QCD the data favor a scale representative of the hard scattering rather than a softer scale of the order of the third jet's transverse momentum. The preferred scale is [mu][sub R][approx]1/4 H[sub T].