Insure versus ensure - which word is the most appropriate in which context? The two words appear to have identical meanings on many levels, but there are some important subtle differences. This article explores the history of the words, highlighting their divergences and similarities.
The prefixes en- and in- mean basically the same thing. In- was the Latin prefix meaning "into". When adapted into Old French, the Frankish language which was basically dominated by Vulgar Latin with a small input of Germanic and Gaelic, in- became en-. When again adapted into English, it was common for the Old French variations to be reconverted back to the Latin originals. This trend was not applied rigorously, hence the existence in English of a few curious pairs like inquire and enquire, both meaning the same thing. As the French language developed however, the prefix en- did not maintain a stable meaning. Instead, it accumulated some other senses, one of which was "to make". This has survived in modern English verbs like endear and encourage.
The introduction of "ensure" and "insure" into English
The late 14th century, French verb enseurer, combining the prefix en- with seur ("sure"), meant "to make sure". Enseurer was related to the other Old French word asseurer, which stemmed from the Latin prefix ad-, meaning "to" or "toward", and again seur. These two words were transmitted to English as ensure and assure respectively. Following the pattern described above, insure was created in the middle of the 15th century as an identical variation of ensure, harking back to the original Latin prefix. The verb assure, however, accumulated an additional meaning, "to make sure/protect against damage by financial payments". In the 1630s, this meaning was adopted by insure instead, which replaced assure in this sense. For ensure, the definition never changed, it always meant and continues to mean "to make sure".
Ensure and insure in modern English
Now that we understand the origins of the two words, should we use insure or ensure? To define ensure has never been a difficult task. The meaning "to make sure" leaps out from its etymological history, and it can be used in exactly this sense with no variation. Regarding insure, the definition is clear concerning its primary meaning - it is the same as ensure. The words can be used interchangeably in this sense. Its secondary meaning, however, "to make sure/protect against damage by financial payments", stems from cultural developments and not etymological trends. The important point is this: if your context demands a word meaning "to make sure", you can use either ensure or insure. However, if your context demands a word relating to protection against damage by making payments, you can use insure only.