I do not find it is a good subject for a silhouette because it is not readable without any details: I know he is a thinker from the title, but I cannot see it.
I like the idea, i think a slightly different angle so you could see more of the hand on the chin would've made this work a little better, just my 2 cents :)
That's a strrrrrrrrrrrrrreeeeeeeeeeeetttttttccccccchhhhhhhh.
The classic thinker pose might have been more believable.
Not sure how comfortable your model would have been with sitting around naked outside though...
It's very hard to see details (like the hand in front of the face) with silhouettes -- results in an indistinct shadow where the viewer can't really see what's going on. The title helps a bit with this, but maybe shooting more in profile would have worked better for you?