All works of scientific style, in particular, in the style of exact sciences, contain a large number of complex sentences. Many of them are multi-component. Of particular interest for the study are the constructions of heterogeneous subordination. They have large “pictorial” means, making it possible to convey the author’s complicated thought in a form that is easy enough for perception. The complex structure breaks down into separate components, allowing the reader to follow the course of logical reasoning, which is of key importance when reading and thinking about sophisticated mathematised texts. However, it would be a mistake to imagine the studied constructions as simply separate predicative parts composed with each other. A complex sentence, built from many components, is a complex “organism” with its own syntactic relations, with a common modality and a predominant connection of structural parts. The subject of this article is constructions consisting of only three components – the main part, the causal subordinate clause and the subordinate clause of the indivisible type. In the style of exact sciences, the causal component makes it possible to clearly establish the cause-and-effect relationship between phenomena, and the entire structure promotes an adequate understanding of complex scientific thought, focusing the reader’s attention on the important points of the presentation of the material. The study was conducted on a number of works by famous modern mathematicians. Their books and textbooks are written in classical mathematical language and are deservedly popular with students and young scientists. In the studied constructions, the causal component can be combined with the component of the indivisible type in different ways. Almost always, the causal component precedes the subordinate clause of the indivisible type and is joined by the conjunctions as and since. When a pronominal-conjunctional correlative subordinate clause acts as a component of the indivisible type, the causal meaning of the entire construction is significantly enhanced. Explanatory and substantive-attributive subordinate clauses lose their independence and are strongly united with the main one in structure and meaning. The construction of the studied constructions turns out to be harmonious: the theme-rheme division of a sentence almost always corresponds to the division of the construction into a subordinate causal clause and a complex main clause. This helps the reader correctly determine the vector of movement of the author’s thought.