I am not bringing this up to deride or disparage Justin Trudeau's command of English, since he possesses a high level of bilingualism that most of us can only envy.
Rather, I find it an interesting question: why DO we say "air" and not "hair" for "heir", especially considering that the etymologically related "heritage" and "inherit" are both pronounced with "hair"? One can never accuse English of being consistent!
"Heir" is in fact one of only four words in standard English (along with their derivatives) starting with a silent "h:. The other three are "honest", "honour", and "hour" (in some varieties of English, "herb", "human", "huge", and "humour" are also on the list). These prove particularly tricky for francophones, who never pronounce "h" in their own language and work very hard to do so in English...only to discover that we've stuck some into our language that aren't pronounced. It must seem like a wily trap, especially for those making solemn oaths in front of millions of people.
All these words share the same history, tracing back to Latin words written and pronounced with an "h". In the case of "heir", the Latin word was hēres. By the end of the Latin era, though, the initial "h" was no longer pronounced, so when Latin evolved into Old French, the word became eir. Legal terms were one of the big categories of words we borrowed from the Normans, so English acquired "eir". No "h" in the pronunciation or the spelling.
But in the Renaissance, there was a move in English to reflect the Latin origins of our words by re-inserting letters into the spelling that had been there in Latin but had long since been lost. This phenomenon accounts for many of our silent letters (for links to other examples see the end of this post). "Eir" became "heir", but we still didn't pronounce the "h".
"Inherit" and "heritage" travelled the same path, starting out in Middle English as "inerit" (ultimately from Latin hērēditāre) and "eritage" (ultimately from Latin hereditagium). Under the combined influence of mass literacy and the social opprobrium reserved for English speakers who "drop their aitches", we started pronouncing the re-inserted "h" in "inherit" and "heritage" (as well as in many other words like "humble", "history", "habit" and so on). But we never did so, oddly, with "heir". How long can "heir" keep up this rearguard action before it succumbs to the pressure of analogy, which in its case is threefold:
all the other words in English starting with "h"
all the other words that have reacquired the Latin "h" in their pronunciation
its etymological cousins "inherit" and "heritage".Perhaps Justin Trudeau is just a man ahead of his time.
Other silent letters in English (click on the links):
"h" in "school" and "schedule"
"h" in "Katherine" and "Anthony"
"g" in "reign"
"p" in "ptarmigan"
"c" in "muscle"
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