Read Print > Gilbert Keith Chesterton > The Innocence of Father Brown > The Secret Garden
Here is a more complete excerpt:
"Yes," said the motionless priest, "it was done so as to make you assume exactly the one simple falsehood that you did assume. It was done to make you take for granted that the head belonged to the body."
The borderland of the brain, where all the monsters are made, moved horribly in the Gaelic O'Brien. He felt the chaotic presence of all the horse-men and fish-women that man's unnatural fancy has begotten. A voice older than his first fathers seemed saying in his ear: "Keep out of the monstrous garden where grows the tree with double fruit. Avoid the evil garden where died the man with two heads." Yet, while these shameful symbolic shapes passed across the ancient mirror of his Irish soul, his Frenchified intellect was quite alert, and was watching the odd priest as closely and incredulously as all the rest.
Father Brown had turned round at last, and stood against the window, with his face in dense shadow; but even in that shadow they could see it was pale as ashes. Nevertheless, he spoke quite sensibly, as if there were no Gaelic souls on earth.
"Gentlemen," he said, "you did not find the strange body of Becker in the garden. You did not find any strange body in the garden. In face of Dr. Simon's rationalism, I still affirm that Becker was only partly present. Look here!" (pointing to the black bulk of the mysterious corpse) "you never saw that man in your lives. Did you ever see this man?"
He rapidly rolled away the bald, yellow head of the unknown, and put in its place the white-maned head beside it. And there, complete, unified, unmistakable, lay Julius K. Brayne.
"The murderer," went on Brown quietly, "hacked off his enemy's head and flung the sword far over the wall. But he was too clever to fling the sword only. He flung the head over the wall also. Then he had only to clap on another head to the corpse, and (as he insisted on a private inquest) you all imagined a totally new man."
The quote is from a novel by G.K. Chesterton, The Innocence of Father Brown.
Father Brown is putting forth his theory that the murdered body in the garden was put together from the head of one man and the torso/legs of another. So, in this case, Father Brown means quite literally that the man in question was 'only partly present'.
Often, the phrase 'only partly present' means that someone is physically present, but s/he is mentally somewhere else, daydreaming or absorbed in his/her own thoughts.
I hope this is helpful,