Focusing on the problem of so called dispositional properties, the paper confronts the time slice type of ontology which Hume's rejection of the idea of necessary connection seems to amount to with the type whose ultimate entities are persisting and changing objects in the notion of which the transtemporal identity and the kinds of changing are already implied. This ontological scheme is shown to be correlated to the explanations in terms of nature of an object, and since this nature is specified by the actions and reactions, necessary for something to be an object of certain kind, the relation between existence and causal efficiency proves to be analytical. Thus the idea of necessary connection becomes justified both from ontological and e...