Independent clauses can stand alone as sentences. To be independent, a clause must contain a verb and a subject and not begin with a subordinating word or phrase.
Some clauses contain a verb and a subject but begin with a subordinating word or phrase (such as because or while) that expresses a close connection to another clause. Such subordinating elements convert clauses into dependent clauses, which cannot stand alone as sentences.
A sentence must contain at least one independent clause; it may contain one or more dependent clauses. The independent clause in the sentence is called the main clause. See also Sentence Types.
Although the pace of technological innovation has been impressively brisk,
whether the materials will make an impact on commerce remains
unclear. [The clause in italics is the independent clause.]
--"Trends in Materials Science," Scientific American
