Another note of caution is required with regard to dialect boundaries. The drawing of isoglosses and dialect boundaries is quite useful in establishing a broad view of regional dialects, but it tends to obscure the fact that, at most dialect boundary areas, one dialect or language variety merges into another. Keeping this in mind, we can view regional variation as existing along a dialect continuum rather than as having sharp breaks from one region to the next.

A very similar type of continuum can occur with related languages existing on either side of a political border. As you travel from Holland into Germany, you will find concentrations of Dutch speakers giving way to areas near the border where “Dutch” may sound more like “Deutsch” because the Dutch dialects and the German dialects are less clearly differentiated. Then, as you travel into Germany, greater concentrations of distinctly German speakers occur.

Speakers who move back and forth across this border area, using different varieties with some ease, may be described as bidialectal (i.e. “speaking two dialects”). Most of us grow up with some form of bidialectalism, speaking one dialect “in the street” among family and friends, and having to learn another dialect “in school.” However, in some places, there are different languages used in the street and in school. When we talk about people knowing two distinct languages, we describe them as bilingual.