At the beginning of this book I raised two main questions. The first was whether multilinguals should be considered as learners and speakers in their own right as opposed to L2 learners or bilinguals, and therefore whether a more explicit distinction between Second Language Acquisition and Third or Additional Language Acquisition is warranted. The second question was how proficient in a non-native language L2 learners are supposed to be before they can begin to be classified as L3 learners in empirical research.

The first question was raised because the language acquisition and the speech production literature treat multilingual phenomena according to two basic assumptions. On the one hand, we have scholars who assume there is no meaningful difference between bilinguals' and multilinguals' processes and accordingly classify all speakers of one or more non-native language as L2 learners or speakers, especially when proficiency in the previously learned non-native languages is low. On the other, we have scholars who argue that this position is not acceptable, as meaningful differences between these learners' processes exist and must be accounted for. The book then set out to examine the empirical evidence in favour of both positions.

All considered, the end balance is in favour of the view that a difference between the two types of speakers exists, as prior linguistic knowledge has been repeatedly shown to affect multilinguals' processes in a number of ways. Clearly, multilinguals have more knowledge that can be used and drawn upon during the acquisition and production process which bilinguals do not have at their disposal, and this additional knowledge seems to play more of a central role than was previously assumed. While the book has attempted to highlight why a difference between Second Language Acquisition and Third or Additional Language Acquisition is warranted, it must be noted that clear empirical evidence in support of the no-difference assumption was not found.