Hello, all.

Native speakers have frequenly corrected my questions worded
like "How to stroke a cat?", saying that this is not a  com-
plete  sentence, but a phrase, which may work only without a
question mark as a title to a chapter in the cat man page.

What say you, then, to the following question from Dunsany's
"King  of  Elfland's  Daughter" -- the  most  poetic work of
prose about the Good people (followed  closely  by  Machen's
"The White People"):

   Sorrowfully then that parliament of Erl saw that their
   plans to have a magic lord had failed; they  were  all
   old  men,  and  the hope that they had had for so long
   being gone they turned less easily to newer plans than
   they had to the plan that they made so long ago.  What
   should they do now, they  said?  How  come  by  magic?
   What could they do that the world should remember Erl?
   Twelve old men without magic.   They  sat  there  over
   their mead, and it could not lighten their sadness.

If "How to come by magic?" is not grammatical, why "How come
by magic?" is?  How explain this difference?

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