In many bilingual communities of Puerto Rican Americans living in the mainland United States, people use both English and Spanish in a single conversation, alternating between them smoothly and frequently even within the same sentence. This practice—called code-switching—is common in bilingual populations. While there are some cases that cannot currently be explained, in the vast majority of cases subtle factors, either situational or rhetorical, explain the use of code-switching.

Linguists say that most code-switching among Puerto Rican Americans is sensitive to the social contexts, which researchers refer to as domains, in which conversations take place. The main conversational factors influencing the occurrence of code-switching are setting, participants, and topic. When these go together naturally they are said to be congruent; a set of three such congruent factors constitutes a conversational situation. Linguists studying the choice between Spanish and English among a group of Puerto Rican American high school students classified their conversational situations into five domains: family, friendship, religion, education, and employment. To test the effects of these domains on code-switching, researchers developed a list of hypothetical situations made up of two of the three congruent factors, or of two incongruent factors, approximating an interaction in one of the five domains. The researchers asked the students to determine the third factor and to choose which mix of language—on a continuum from all English to all Spanish—they would use in that situation. When given two congruent factors, the students easily supplied the third congruent factor and strongly agreed among themselves about which mix they would use. For instance, for the factors of participants "parent and child" and the topic "how to be a good son or daughter," the congruent setting chosen was "home" and the language mix chosen was Spanish only. In contrast, incongruent factors such as the participants "priest and parishioner" and the setting "beach" yielded less agreement on the third factor of topic and on language choice.

But situational factors do not account for all code-switching; it occurs even when the domain would lead one not to expect it. In these cases, one language tends to be the primary one, while the other is used only sparingly to achieve certain rhetorical effects. Often the switches are so subtle that the speakers themselves are not aware of them. This was the case with a study of a family of Puerto Rican Americans in another community. Family members believed they used only English at home, but their taped conversations occasionally contained some Spanish, with no change in situational factors. When asked what the presence of Spanish signified, they commented that it was used to express certain attitudes such as intimacy or humor more emphatically.