continual, continuous

Most usage guides make the following distinction between these two terms.

Continual describes an activity that occurs repeatedly, but with intermittent breaks.

• The continual sound of traffic outside her new apartment kept Joyce awake the first night.
• Reading was a continual source of enjoyment for Rashid during his long recovery.

Continuous describes something that occurs without a break in time or in space.

• The continuous flow of water has worn away the rock and deepened the streambed.
• In every direction, the desert sand stretched in a continuous expanse to the horizon.

The same distinction exists, of course, for the adverbs continually and continuously:

• The traffic surveillance camera taped continuously as the cars continually moved past.

Usage note

Be careful not to use continuous (uninterrupted) when you mean continual (constantly repeated):

• Sadie’s continual (not continuous) complaining began to get on her co-workers’ nerves.

Sadie might have complained constantly—but she couldn’t have complained without interruption (she must have spent some time working, and no doubt she went home at night). Therefore, continual is the word needed here.

Tip

In Garner’s Modern American Usage, Bryan Garner suggests this handy trick to remember that continuous means “without interruption”: think of the ending -ous as standing for “one uninterrupted sequence.”