To convince someone that what he really sees is sense-data, it won’t do to ply him with arguments while he is doubtful about what he sees. If he questions his own eyes, he will be in no receptive state for your gospel—your good news about a medium of unvarnished news. You can insist; he will blink and rub his eyes. He takes himself to be in a poor position to see something. You do not aid him by insisting that he is a perfect position to see something poor. He wants to move closer, to turn on a light, to visit an optometrist. You want him to listen to argument. To convince him you need him convicted by his sight. He needs to take himself to be in optimal conditions for seeing. He should stare and not blink; rub his head and not his eyes. He should not doubt his eyes; he should doubt sans phrase. He should not feel compelled to move closer, to turn on a light or to visit an optometrist. He should listen to your argument while staring fixedly at whatever he takes himself to see. Sense-data only show themselves to doubt sans phrase. Seeing them requires vision mixed with argument. They hide themselves from someone who simply doubts his eyes.