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Q From Bob Leavitt: In the 1940s my high-school chemistry teacher dad noted a change in the wording for a substance that would easily burn: inflammable became flammable. Why did this happen? Is the use unchanged in the UK? Or is it still changing? Or maybe we Americans are incorrect? Or maybe it makes no difference?

A The problem with inflammable is the in- at the front. English has many words in which it means “without” or “not”. A majority have been imported from Latin with the prefix already attached, such as infertile and inarticulate. Others, such as inexpensive and invariable, have had it added in English. We don’t turn words into their negatives using in- any more; we prefer un- or non-, or sometimes a-, but the aura of negativity surrounding in- is still very strong in our minds.

Unfortunately, Latin had another in- prefix, whose root sense was the same as English in but which could sometimes strengthen the meaning of the word it was attached to, as in indoctrinate and incantation and also in inflammable. This is much less common or obvious, so much so that inflammable can all too easily be taken to mean “not capable of burning”, when it really means “very easily set on fire”.

It’s impossible to establish how often confusion over inflammable led to accidents but evidence exists in US newspapers more than a century ago of the mistaken meaning of inflammable:

These bricks are said to be light, impervious to wet and utterly inflammable.

Davenport Daily Leader, 29 Jan. 1892.

[The dresses] will be rendered almost inflammable, or at least will with difficulty take fire, and if they do, will burn without flame.

Nashua Reporter, 30 Jul. 1903.

This confusion has survived to the present day. A US study published in 2010, Hazard Connotation of Fire Safety Terms, by Michael S Wogalter and others, found this to be so among American adults: “Inflammable has the same meaning as Flammable but was rated as if it was of very low flammability, consistent with previous research.”

From the beginning of the twentieth century the potential confusion started to worry American safety experts and insurance companies. Under their urging, flammable had begun to appear in safety advice and local bylaws in the first decade of the century but it was then a technical term unknown to the wider public. In 1920, they ran a campaign to try to change the language. This notice appeared widely in technical journals:

The National Safety Council, The National Fire Protection Association, and similar organizations have set out to discourage the use of the word “inflammable” and to encourage the use of the word “flammable” instead. The reason for this change is that the meaning of “inflammable” has so often been misinterpreted.

It was convenient that these bodies had words with which to replace the potentially disastrous ones. Flammable had been created early in the nineteenth century from the same Latin verb flammāre, to set on fire, that’s also the source of inflammable; flammability had appeared two centuries earlier still. Though they had never caught on, they were available to be resurrected. Advocates also preferred non-flammable to non-inflammable. Perhaps strangely, non-flammable preceded flammable in the US by about a decade. It did so earlier still in the UK, where it was a term of art in naval gunnery as early as 1888.

Despite this early effort, progress was slow. Flammable really only started to take hold in the US from the 1950s. For example, the official shift from inflammable to flammable on fuel trucks took place as recently as 1964. Purists hated the change, ranting at the time that the fine literary word inflammable was being replaced by a corrupt form, an unnecessary dumbing down of language in order to accommodate the ignorance of the great unwashed. Objections died out eventually and Americans are now more likely to use flammable than inflammable both in speech and writing, substantially more so than Australians, Canadians or Britons.

In Australia, flammable began to appear only in the 1960s. The first modern example of flammable that I can find in British usage is dated 1952 and it wasn’t until 1959 that the British Standards Institution issued the following advice: “In order to avoid any possible ambiguity, it is the Institution’s policy to encourage the use of the terms ‘flammable’ and ‘non-flammable’ rather than ‘inflammable’ and ‘non-inflammable’.”

The use of flammable and non-flammable in technical contexts is now universal. However, flammable is still not fully accepted in everyday speech and even where it is, confusion remains about the technical difference in meaning between it and combustible. Many people think the latter is a more severe state than the former but in fact the reverse is true.

The figurative senses of inflammable and its relatives and the medical application of inflammation are unaffected, since they don't have the same safety implications.

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