Well several.
1) Vu Ja De - the effect of seeing the familiar with fresh eyes. - when in doubt, seize the vu ja de

2) Procrastination (divergence) - if the project is left open/unfinished for long enough, new ideas and thoughts come to mind. This is how I did a lot (not all) of my songs. I had an enveope or book with the (provisional) title encircled in the centre, with related words/phrases around it and more around them. Apparently we close our minds as the project finishes.

3) Rationalisation (convergence) - at some time verses/chorus can spring to mind and be written down, and inspected for scansion/rhythm, rhyme/better rhyme. After which the direction of the theme becomes clear and more text follows (ie 2)).

4) Fully Formed - Have you considered this may be a life long procrastination bursting out? It could be a project that has no theme only a goal, like writing a song that people would think was traditional. Then one day Vu Ja De happens and the collected knowledge on the theme presented comes pouring out.

Adam Grant on original thinkers at TED.com has a few insights one of which is that there is a sweet spot of procrastination that produces the most original and successful ideas. Too little and the result is predictable, too much and it never gets done. And it is the diversionary tactics that give us time and data and unconscious cogitation that feeds the creative process. When in doubt, seize the vu ja de

TED radio Hour (BBC.co.uk) (54 mins) which triggered my thoughts on the above. Some of it may be available in the USA at npr.org>originals ... how to spot one (20 mins). I can't find the other bits of it.

And throw in the Zeigarnik Effect that postulates we recall unfinished tasks better than completed ones.

Also In the mid of a master procrastinator Tim Urban on TED.com