With examples from Burn Notice.
It’s tough to differentiate between continuous and continual, the adjective form of the words, or continuously and continually, the adverb form, because even the dictionary definitions seem to define them in very similar ways. For example, merriam-webster.com defines continuous as “marked by uninterrupted extension in space, time, or sequence,” and continual as “continuing indefinitely in time without interruption.” The definitions are not identical, but are close enough to be very confusing.
However, while both words apply to things being ongoing, if something is continuous it occurs without interruption. If something is continual it occurs regularly over a period of time. This can best be demonstrated with some examples.
Even with Michael’s extensive experience with surveillance, he found the continuous drone emitted by the radio receiver made it difficult to concentrate.The usage is the same for the adverb continuously:
The con artist they had captured begged for mercy continuously until tasered into silence by Fiona.An example of continual might apply more to a process which is done regularly:
Michael had always believed that the continual need to replace batteries in bugs resulted in more operatives being captured than any other reason.Or something which happens on an ongoing basis:
Fiona was becoming increasingly frustrated with Sam continually asking for her advice on patching up his relationships.So even though continual refers to something which happens regularly, these events aren’t uninterrupted, which is the core of the difference between continual and continuous.
Dr Grammar suggests that instead of using continually it may be better to use intermittently or periodically in order to emphasise the distinction with continuously, but unless it's important to make that distinction, this isn’t necessary. What is important to remember is that something is continuous if it is unceasing, while something is continual if it occurs repeatedly.