This study tests the applicability of the Complexity Principle (Rohdenburg 1996) and the Uniform Information Density Principle (Jaeger 2010) on adjectival data as regards the variation between retaining and omitting the complementizer that in English adjectival complementation constructions. More specifically, the study tests the effect of different factors of potential importance on this variation across extraposed (e.g. It was inevitable (that) he should be nicknamed 'the Ferret') and post-predicate clauses (e.g. I'm happy (that) we are married). While both the factors concerned with the Complexity Principle and the Uniform Information Density Principle are found to have an effect on post-predicate clauses, less clear effects are found concerning extraposed clauses. I attribute these findings to the difference between the two constructions in terms of their frequency of co-occurrence with different matrix subject types and with different adjectives.