One group of academics argues for the maximal definition which means speakers are as proficient in one language as they are in others and have as much knowledge of and control over one language as they have of the others. Another group of academics argues for the minimal definition, based on use. Tourists, who successfully communicate phrases and ideas while not fluent in a language, may be seen as bilingual according to this group.

However, problems may arise with these definitions as they do not specify how much knowledge of a language is required to be classified as bilingual. As a result, since most speakers do not achieve the maximal ideal, language learners may come to be seen as deficient and by extension, language teaching may come to be seen as a failure. One does not expect children to "speak chemistry" or to have become a professional athlete by the time they have left school, yet for graduating school children anything less than fluency in a second language could be seen as inadequate. 

Since 1992, Cook has argued that most multilingual speakers fall somewhere between minimal and maximal definitions. Cook calls these people "multi-competent".

Comparing multilingual speakers
Definition of multilingualism
Multilingualism between different language speakers
Multilingualism at the linguistic level