Lately I have been pondering a great deal upon the nature and quality of inspiration, particularly poetic.
The Talmud's distinction between psalms that begin "A song for David" and those that begin "For David, a song" is fascinating. When the inspiration comes first, the song precedes the name. When the person has to begin writing before the inspiration is quite there, then the name comes first.
It would be interesting to hear from other writers about the times the spirit moves them to write as opposed to the times they are obligated to start writing without being yet in the mood.