He derives the authority of his work from painting in front of the subject on Thames-side footpaths and other vantage points, and from struggling to turn paint into prospect while having the constant challenge of the actual view in front of him. Like a philosopher, he is seeking after truth, and unsparing in his scrutiny. A central problem facing a realist painter who chooses the river for subject is articulating and making sense of a large plane of water. Pemberton manages to convey to the viewer a sense of travelling across it: not just in terms of looking, but in imagining the passage of a boat over it, so well does he make the scene real and vivid.