Grosjean (1997) explained the complementarity principle as being the function of language and the use or dominance of languages used by a speaker. This dominance in certain domains of life (e.g. school, home, work, etc.) can be influenced by crosslinguistic information. One such study found that crosslinguistic influence was occurring within the speech of the studied bilinguals, but the intensity of influence was subjective to the domains of speech being used (Dopke, 1998; Muller, 1998; Yip and Matthews, 2000; Muller and Hulk, 2001). Argyri and Sorace (2007) found, much like many other researchers, that language dominance plays a role in the directionality of crosslinguistic influence. These researchers found that the English dominant bilinguals had influence of English on their Greek (concerning preverbal subjects specifically, but also the language in general), but not from their Greek to their English; contrarily however, the Greek dominant bilinguals did not show evidence of Greek influence on their English (Argyri and Sorace, 2007). This then lends way to both support of language dominance and opposition. One thought is that bilinguals who do not receive sufficient exposure to both languages, or in this case their ‘weaker’ language, and do not exhibit crosslinguistic effects because their dominant language is much more advanced. This lends to the idea of input frequency accounting for effects of crosslinguistic influences and the use of dominance in differentiated domains to strengthen or weaken susceptibility to this influence. Also, should influence such as English preverbal subjects not be found in this instance of Greek, then instead of omitting this learned aspect of language, the speakers will use it. This raises the question of use, input, and similarities versus differences between the languages used.
Some researchers believe that CLI may be a resulting effect of contact-variety input, or linguistic input from a person whose language has already been affected by another language (Hauser-Grüdl, Guerra, Witzmann, Leray, & Müller, 2010). This is to say that the environment in which one is learning another language can influence what is actually being learned. Take for example the fact that most L2 learners are receiving input or teachings from similarly speaking bilinguals (same L1/L2), Hauser-Grüdl, Guerra, Witzmann, Leray, and Müller (2010) believe that the language being taught has already been influenced by the other in the teacher’s mind and therefore the input the learner is receiving will exhibit influence. These researchers believe that the L2 learners will replicate influences from their instructor because their input of the L2 is not as pure as input from a monolingual This theory compelling people to believe that all L2 learning is affected by CLI from the very start of their input, however, is not a well supported theory of CLI or its function in L2 acquisition.
Other researchers believe that CLI is more than production influences, claiming that this linguistic exchange can impact other factors of a learner’s self. Jarvis and Pavlenko (2008) described such affected areas as experiences, knowledge, cognitions, development, attention and language use, to name a few, as being major centers for change because of CLI. These ideas suggest that crosslinguistic influence of syntactic, morphological, or phonological changes may just be the surface of one language’s influence on the other, and CLI is instead a different developmental use of one’s brain (Jarvis and Pavlenko, 2008).