as when a carpenter needs an adze; or material, as when a carpenter needs wood; or minerals, as when a sawyer needs another sawyer; or a particular time, as when a person needs summer; or a motive, as when someone eating needs hunger; or the removal of an impediment, as when a washerman needs the cloud cover to clear.

The nonexistence of the effect depends upon the cause’s not being in the state in which it is actually a cause, whether the cause itself exists in some other state or does not exist at all. Thus, if there is no external impediment and the agent itself exists, but is not a cause by virtue of its essence, the existence of the effect depends upon the presence of the aforementioned state. When that state is present—whether it consists in a nature, a decisive will, or something else—the effect must exist. If that state is absent, there must be