In a language like English a subject must be overtly lexicalized in the sentential I domain. Northern Italian dialects lexicalize the same position by subject clitics; subject noun phrases are in a higher position, combining with subject clitics and preceding them. Hybrid types also exist, alternating between subject clitics and noun phrases, like French. By contrast, in a language such as Italian no subject is lexicalized in the sentential I domain. These parameters are formalized in the following sections.