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I came across the sentence "At what age were you able to start reading successfully to a baby?". My question is why the word " at " can be placed at the beginning of the sentence? Is the sentence the same as "how old were you able to start reading successfully to a baby?" I often see questions begin with "what", "how", "when", "why", and "what". It's the first time I notice the sentence which begins with "At what age". Can anyone explain why it is like this? What is the grammar rule that the sentence follows? Thanks in advance.

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  • “How old were you able...” is ungrammatical. “At what age” is correct.
    – user 66974
    Jun 1 '20 at 9:27
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    "At what age" is an adverbial phrase comprised of {preposition at + noun phrase what age}. We can replace it with the adverb "When". Adverbs and adverbial phrases are commonly used to start sentences.
    – Greybeard
    Jun 1 '20 at 9:36
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    'At what time did the thunderstorm begin?' // 'At what point did you decide to leave?' // 'For what reason did she take the French subsidiary?' // 'To which countries do they fly?' // 'Among which tribes is this still a custom?' // 'Beneath which stone did the crab hide?' // 'Concerning which regulations is there a problem?' // 'On top of which box was the spider?' ... Jun 1 '20 at 14:50
  • Thank you. I do need to improve my grammar.
    – Kindly
    Jun 1 '20 at 17:01
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Leaving aside the problem of whose age (the addressee's or the baby's) is being questioned,

  • At what age were you able to start reading successfully to a baby?

is an example of a grammatical phenomenon known as Pied-Piping. This sentence is a question, formed from a statement something like

  • You were able to start reading successfully to a baby at ___ age

where the blank represents the missing information the questioner is seeking; in this case it gets transformed into the interrogative what in the prepositional phrase at what age.

  • You were able to start reading successfully to a baby at what age

The next step in question formation is to invert (exchange) the subject (you) and the first auxiliary verb (were)

  • Were you able to start reading successfully to a baby at what age

If it weren't for the Wh-word at the end, this would be an OK yes/no question

  • Were you able to start reading successfully to a baby at that age?

But it's a Wh-question, not a yes/no question, so after inverting, the next step is to move the Wh-word (in this case, the phrase what age) to the front of the question, producing

  • What age were you able to start reading successfully to a baby at?

Which is grammatical, but is also a great example of stranding a preposition at the end of the sentence. What good is it doing there? It doesn't mean anything; it's just something required by the idiom be at X age, and it's silly to require the speaker to add it at the end, or for the listener to have to wait for it. But you can't leave it out. Because grammar.

So, the optional rule of Pied-Piping allows the speaker to move the whole prepositional phrase at what age, as a unit interrogative constituent.

Not only that, but any other higher constituent that the interrogative word is part of -- like a noun phrase containing the prepositional phrase, or another noun phrase containing that one -- can also be pied-piped, at the will of the speaker, producing prose of massive turgidity, like

  • printed volumes the lettering on the covers of which is specified by law

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