 Available to Hartley were both Locke’s distinction between “simple” and “complex” and also instances in which the de- prefix meant “further.” On the analogy of “compound” to “decompound,” he wrote of ideas and actions being either “complex” or “decomplex.” In Hartley’s theory, the associations in a complex action or idea are synchronic, while the associations in a decomplex action or idea are diachronic. In playing a piano, hitting the D key at the sight of the printed note D is a complex movement, while playing a composition is a decomplex action.