What was the cosmological argument, and what is the problem (weakness) with it?
The cosmological argument is a category of argument with a number of version put forth by various philosophers, including Thomas Aquinas. The cosmological argument states, briefly, that there is not an infinite range of causes of any one event: the number of causes for a thing are limited in number. For example, a cat and a leaf can cause a scratch though clouds cannot.
Within this causation, things that exist have come into existence from a limited range of causes. Since they cannot cease to exist, the cause of existence must be external to their intrinsic natures. Going further back, the cause of their existence must also have a cause. Yet, since causes cannot be infinite, at some point something exists that has no cause. The very cosmos itself must also have a cause. In the cosmological argument, this cosmological cause is the final, finite cause beyond which there are no further causes. The argument associates this final, finite cause with a supreme power or being, in other words, with God.
One weakness with this argument relates to the term "necessary being." The "necessary being" of the argument is defined as one that cannot call itself into existence without already existing: if it exists, it must continue to exist; if it does not exist, it cannot initiate existence. This is not "self-contradictory" therefore is a sound definition. Yet some, like Kant, argue that the term be defined as meaning existence that is logically necessary, or "logically undeniable." Since no proof is at hand for a logically undeniable necessary existence of a superior power or being--a final, finite cause--the cosmological argument is thus construed as weak.
The Cosmological Argument is a standfard argument for the existence of God, expounded by the theologian Thomas Aquinas, (1225-1274). The argument is based upon the premise that every being and every event has an existing cause which preceded it. This is accepted as universally true in our world; things do not pop into being from nowhere, and things do not happen for no reason. But if every being and event must be caused by a previous being or event, and that cause in turn must have a cause, it seems as if the line of causes must stretch back into the past infinitely, an idea described as an infinite causal regress. An infinite causal regress is considered an impossible model for understanding the nature of existence because it does not explain how the infinite chain of causes and effects itself came into being. Therefore, how the universe originally began appears to present a problem, since it cannot have been caused by nothing, but if it was caused by something, that thing would have had to have been caused by something else. The Cosmological Argument claims that this problem proves the existence of a First Cause of the universe, which was unique in that it itself did not have to be caused. The First Cause is usually supposed to be the traditional Judeo-Christian God, and thus the argument proves the existence of God.
There are several problems with the cosmological argument. In the first place, the argument is not a hard-and-fast proof of its conclusion, but instead just offers us both a problem, and a conclusion, which, if it were true, would resolve the dilemma. This reasoning is similar to a detective charged with solving a murder pointing out a suspect who plausibly could have committed the crime, and announcing that the mystery is solved, since the murder is now explained. It is true that declaring the suspect guilty "explains" the murder, but this does not mean that it is the true explanation. Likewise, it is true that if we accept the notion of God as an uncaused being, the problem posed by infinite regress vanishes. But this does not mean that it is the true or only solution. In fact, we can only arrive at this conclusion by denying the first and most basic premise - that all things have a prior cause. A good argument does not deny its own premises.
Another problem with the argument is that it doesn't actually explain much of anything. It merely states that the First Cause was uncaused, but not how or why this could be possible. Why the "first cause which existed uncaused" is any different from a concept of the universe itself simply beginning uncaused is not clear.
Finally, the argument does not prove that the First Cause is identical to the tradional God. Since the only thing the argument claims to prove about the First Cause is that it, A), was uncaused, and B), caused everything else, it does not follow from this that it has any of the other attributes of God. It is quite possible even to concieve of a First Cause which has since ceased to exist.