Although continuous and continual appear to be synonyms, they are not. However, the differences are subtle, not clear-cut. Both words are common in research papers, especially in the materials and methods section, where the distinction can be important. For example, seeds that were continually exposed to freezing temperatures will behave differently from those that were continuously exposed to freezing temperatures.
Let us consider the difference between the two words on three counts, namely, whether the process they describe has a clear beginning or end, whether the process ever stops, and whether the words describe a physical object. Again, a few examples will help.
Continuous usually implies a distinct beginning or end. Heat treatment, for instance, has a point at which it begins and another at which it ends, as in "The solution was maintained at 45 °C for 25 min," which means that the solution was continuously exposed to that temperature for 25 minutes.
Continuous implies an uninterrupted process. A continuous pain is that which never goes away (unlike a throbbing pain, for example); a continuous flow means a ceaseless flow; a continuous pressure means the pressure is never taken off.
Continuous can be used to describe physical objects. A continuous line in a line chart, for example, is different from a dotted line: the former has no gaps whereas the latter comprises dots separated with space. A continuous surface has no gaps. Continual is never used to describe physical objects but refers only to a process or duration.
Although the difference between the two words may be clearer now, you could always avoid them; Burchfield's advice in The New Fowler's Modern English Usage  is that it is often better to use such alternatives as recurrent or intermittent for continual, and unbroken, uninterrupted, or incessant for continuous.
 Burchfield R W (ed.). 1996. The New Fowler's Modern English Usage, p. 178. Oxford: Clarendon Press. 864 pp.
["Publish and prosper" is a series of posts about tips for researchers whose first language is not English but who submit papers to journals published in English. The series touches upon not only writing (spelling, grammar, punctuation, usage, and style) but everything else relevant to publishing research papers that journal editors wish their authors knew.]
|Yateendra Joshi is a publishing consultant with Editage. To read other articles by Yateendra, click here.|