If one model is much weaker than the other, linear interpolation will typically produce a model of intermediate strength (i.e., worse than the better model), with the weaker model contributing a form of smoothing at best.
based on equation 13, we express our semantic probabilities as the product of the unigram probability, p(w), and a semantic component, ∆, which determines the factor by which this probability should be scaled up or down given the context in which it occurs.