The English language is full of words that are both similar in sound and similar in meaning. Many of these words are classified as homophones, but many others don’t quite fit under that label. The two words continually vs. continuously, while not being exact homophones, sound enough alike to confuse writers. Plus, their meanings are somewhat similar, so it adds a layer of confusion. But, as is the case with so many other words, once you know the difference, picking the correct word, continually or continuously, is easy.
The word continuous originated in mid-17th century: from Latin continuus ‘uninterrupted’, from continere ‘hang together’ (from con- ‘together with’ + tenere ‘hold’) + -ous. The word continual originated from Middle English: from Old French continuel, from continuer ‘continue’, from Latin continuare, from continuus (see continuous).
Continuous as adjective:
Continuous is also used in mathematics (of a function) of which the graph is a smooth unbroken curve, i.e. one such that as the value of x approaches any given value a, the value of f(x) approaches that of f(a) as a limit.
Continual as adjective:
Continuous or continual:
Things that are unceasing or exist without interruption are continuous. For example, the flow of a river, the motion of the planets around the sun, and the heartbeat of a healthy human are continuous because they never pause. Things that occur frequently or recur intermittently are continual. The continual action doesn’t happen ceaselessly, but it does happen regularly. For example, phone calls to a busy office and departures from a bus station are continual because they happen regularly but not in an uninterrupted stream.