As a child, I was allowed to watch as much television on Saturday and Sunday mornings as I pleased.
When I was a child, I was allowed to watch as much television on Saturday and Sunday mornings as I pleased.
Is really "As a child" a proper way to say "When I was a child" in the case above?
As far as I understand, it seems to me that these two expressions are not entirely interchangeable.
Can anybody explain?
As a child will bear this interpretation; but it has other senses. For instance:
As a child, I was not allowed into the bar. ... Here, as a child probably means not when I was a child but because I was a child.
As a child, she supported the laws against internet bullying; as a citizen, she regretted the possible infringement on free speech. ... Here, as a child means in her role as a child (and therefore a potential victim of internet bullying), as opposed to in her role as a citizen (and therefore a potential victim of oppression).
As a child do I follow the precepts of my Master. ... Here, as a child probably means in the manner of a child
So you have to be more careful when using as X in a temporal sense, lest one of these other senses interfere with your readers' understanding. On the other hand, the context will usually make your sense clear, so you don't have to be too careful.
While StoneyB covers meanings of as a child that differ from the meaning shared with when I was a child, the alternate use of when I was a child is not clearly addressed.
When I was a child can be used to describe the speaker as a child, but it can also be used to refer to a particular time.
When I was a child, George Washington was the President of the U.S.
Substituting as a child would mean that George Washington was President during his childhood.
The first one sounds like you're comparing your present condition against the past; while second one is like you are just remembering something from your childhood.
Probably not a descriptive answer
