Latin for first cause or prime cause, a common philosophical argument for the existence of God as the prime mover.

The reasoning is based on the observation that everything has a cause, even the cause has a cause, has a cause, has a cause... Hence, there has to be a first cause, the first link in the chain of causality.

However, there are several problems with this reasoning.

First of all, nothing has a single cause. Every observable phenomenon has more than one cause. Causality is not a chain it is a net.

The assumption that there is a first cause is just that, an assumption. It is just as possible that causality is circular. For that matter, there are other possibilities, some of which we may not even have considered or discovered. Besides, the observation on which this assumption is made shows the exact opposite: No matter how far we go in the "chain", whatever we discover also is caused.

Even if there were a first cause, there is no way to say whether that cause was a person. After all, most phenomena are not caused by a person, nor a group of persons: For example, rain is not caused by someone turning on some heavely faucet. Rather it is a result of a process which includes but is not limited to evaporation of water, accumulation of vapors in cloud formations, condensation, atmospheric pressure, etc. Incidentally, this process is circular, so it is equally as "logical" to say that rain is its own cause as that it is not.

Finally, even if there were a first cause and it were a person, that does not imply that person is perfect, all-knowing, omnipotent, etc - all attributes assigned to God.