"Elaborate" as a transitive verb?

It is common to speak of "elaborating on (or upon) a topic." However, I have been told that this is appropriate only when some explanation has already been given; if no information is yet known, then the proper usage would be "elaborating the topic." Is it true or false?

For example, if the president issued a statement, and I wanted to explain why he did so, I might say, "I would like to elaborate the motive behind the president's statement." It wouldn't be correct to say "elaborate on the motive," since nothing is yet known about the motive.

Yes, there may be a distinction between "elaborate" used with a normal direct object and "elaborate on" used with a prepositional object: the former, where it is used, tends to mean "create, establish", whereas the latter tends to mean "give further details about". If you look at these examples from the Europarl corpus:

http://www.translationexamples.com/ex/en-fr/elaborate

you'll see examples such as:

"must outline a concrete strategy ... and elaborate a detailed investment plan"

where the implication does appear to be create a plan, not develop one already in existence, vs:

"elaborate a little on what you said".

where the idea is "go into more detail".

As an informal intuitive observation, I would have said that the first usage isn't very common. However, I did a quick check on Google ngram and the figures appear to belie my intuition:

If these figures are anything to go by, "elaborate on" appears to be a relatively recent innovation, vs a time when "elaborate" was practically always used with a 'straight' direct object.

Interestingly, as testimony to this being a relatively recent innovation, Websters 1913 edition doesn't appear to mention the possibility of "elaborate" with 'on', but gives the following definition and example of transitive 'elaborate':

"To perfect with painstaking; to improve or refine with labor and study, or by successive operations; as, to elaborate a painting or a literary work."

I stand to be corrected, as ever, but I never heard of this distinction. OP's suggested shift in meaning (only use "on" if the subject has already been partially explained) sounds somewhat fanciful to me. The real difference is that the verb elaborate has two related but distinct meanings, only one of which implies the act of explaining.

This definition from Oxford Advanced Learners Dictionary gives the usages I'm familiar with. For definition 1 (explain something in more detail) the verb is most commonly followed by "on", but this is largely a matter of style. Definition 2 (develop, or add more detail) is never followed by "on".

Here is a paragraph that uses elaborate as a transitive verb three times in one paragraph, where only the last is followed by "on". I believe the writer is quite concious of the two different usages above, and correctly applies them.