 Grounding and ontological dependence are distinct from each other. The simplest way to see this is by means of the kinds of case that revealed to David Lewis that causation is distinct from causal dependence (1973): preemption and overdetermination. Just as cases of causal overdetermination and preemption involve causation without causal dependence, so too do cases of ‘grounding overdetermination’ and ‘grounding preemption’ involve grounding without ontological dependence. For example, the fact that I exist grounds the fact that something exists, but the obtaining of the latter fact does not depend upon the obtaining of the former; the fact that something exists is massively overgrounded.