The study reported here is concerned with how children acquire complex sentences for expressing their beliefs about causally related events, in the transition in language development from simple to complex syntax. Subjects were three girls and four boys, observed longitudinally from 26 to 38 months of age in their homes. Data analysis began with those observations in which each child began to produce causally related propositions without syntactic connectives, and continued until the children were about 3 years old. Two broad categories of causal meaning were expressed in the children's causal statements. Objective meaning concerned means-end and consequence relations that were evidential and fixed in the physical world. Subjective meaning expressed causal connections concerned with personal, affective, or sociocultural beliefs. While most of the children's statements expressed subjective meaning overall, the acquisition of syntactic connectives was associated with objective meaning. These results are discussed in terms of the development of these children's understanding of causality and the acquisition of increasingly complex language.