Final answer:
The key difference is that an adverbial clause contains a subject and a verb and often starts with a subordinating conjunction, while an adverbial phrase lacks a subject and a verb and cannot stand alone as a sentence.
Step-by-step explanation:
The difference between adverbial clauses and adverbial phrases primarily lies in their structure and function within a sentence. An adverbial clause contains a subject and a verb, and it usually begins with a subordinating conjunction (e.g., because, when, although).
Conversely, an adverbial phrase does not contain a subject and a verb and thus cannot stand alone as a sentence. Both adverbial clauses and adverbial phrases function as modifiers providing additional information about time, place, manner, condition, frequency, or degree.
Here is an example of an adverbial clause: Pierre ran quickly through the main points of his argument because he was short on time. The adverbial clause 'because he was short on time' provides a reason for his quickness, with 'because' as the subordinating conjunction, and 'he' and 'was' as the subject and the verb.
Here is an example of an adverbial phrase: She threw down the gauntlet quite suddenly. The phrase 'quite suddenly' is an adverbial phrase that modifies the verb 'threw' and does not contain its own subject and verb.