It is incorrect to use the words continuous and continual interchangeably because there is a difference between them.
|Meaning||For a certain duration, on and off but with interruptions||For a certain duration, uninterrupted|
edit Main Difference in Meaning
While both adjectives describe duration, continuous indicates duration without interruption. For example, The continuous humming of the fluorescent lights gave him a headache.
Continual indicates duration that continues over a long period of time, but with intervals of interruption. For example, The continual street repair disrupted traffic for nearly two years.
The distinction between adverbs continuously and continually follows the same pattern. For example,
- The infant screamed continuously for 2 minutes until her parents woke up to change her diaper. (here continuously means non-stop)
- It drizzles continually in the winter months in Seattle. (continually does not mean it's drizzling non-stop. Rather, it drizzles on and off throughout the winter.)
edit Video explaining the differences