Multiple final embedding of clauses

There are no grammatical limits on multiple final embedding of clauses. But converging corpus data from English, Finnish, German and Swedish show that multiple final embedding is avoided at levels deeper than three levels from the main clause in syntactically simple varieties, and at levels deeper than five levels in complex varieties. The frequency of every successive level of final embedding decreases by a factor of seven down to levels 4–5. Only relative clauses allow free self-embedding, within the limits just mentioned. These restrictions are regularities of language use, stylistic preferences related to the properties of various types of discourse. Ultimately they are explained by cognitive and other properties of the language processing mechanisms. The frequencies of final embedding depths in modern languages such as English and Finnish is not accidental. Ancient Greek had reached this profile by 300 BC, suggesting cross-linguistic generality of the preferences.