St. Thomas Aquinas (1225-1274 AD) wrote a specific series of works in Summa Theologica where he attempted to use logic alone to prove the existence of god. He came up with five arguments, or 'ways', that he felt could logically lead to that one conclusion. Of course, like all god claims, there is no evidence to support the claims, and his arguments have all been thoroughly debunked as containing serious logical flaws and presuppositions.
And yet modern apologists, either knowingly or simply through parallel thinking, use the same arguments to this day as if they are completely bullet-proof. Even professional apologists resort to mere modifications of these ancient debunked arguments by simply adding their personal spin to them. The modern versions are often simply the exact same argument with a few added premises that the apologist feels makes the causal path to the conclusion clearer.
The Five Ways
The five arguments have been restated in English as follows:
The Argument from Motion – a first mover special pleading
The Argument from Cause – a first cause special pleading, something from nothing
The Argument from Contingency – something from nothing
The Argument from Perfection – perfect being must exist
The Argument from Design – anthropic principle
Next will be a detailed deconstruction of the 'Five Ways'. Each section starts with the translated arguments followed then by the refutations specific to the premises and conclusions made. These refutations are highly useful in many arguments with theists given the similarities of theist arguments to these ancient ideas.
The Argument from Motion
Nothing can move itself.
If every object in motion had a mover, then the first object in motion needed a mover.
This first mover is the unmoved mover, called God.
This argument is based on an Aristotelian world-view that maintains an intrinsic identity of an object. Along with this world-view are many completely false beliefs like an aether, or a substance permeating space and that motion belongs to an objects individual description. But there is no unmoving reference frame for objects to pass through and be measured against.
The Michelson Morley experiment, among many others, have demonstrated that no aether exists. Einstein's Special Theory of Relativity demonstrates that motion is entirely relative and a property only of a system of objects requiring at least two things, not a property of any one object.
So as the premise maintains a single body motion relative to a fixed unmoving reference, the argument is flawed as the premise is flawed. The conclusion is also simply an argument from ignorance combined with a special pleading fallacy citing god as the exception to the premise and the only possible explanation if the premise is true.
The Argument from Cause
There exists things that are caused (created) by other things.
Nothing can be the cause of (or create) itself.
There can not be an endless string of objects causing other objects to exist.
Therefore, there must be an uncaused first cause called God.
This relies on a presupposition of things always being created. But nothing is created. Energy only changes forms. And the change of forms can occur without a cause. For example, quantum fluctuations occur. We know they occur and modern electronics would be impossible if they did not occur. Quantum fluctuations are random and unguided. Every now and then a fluctuation can exceed a threshold forcing a change in a system. As the fluctuation is uncaused, the change it creates is uncaused. Particles spring into existence without cause as virtual particle/anti-particle pairs. That is how we get Hawking radiation.
The “something cannot come from nothing” phrase pops up in premises presented by apologists because they lack an understanding of what “nothing” means, or rather how it means something quite different to cosmologists and physicists. In addition, it is an unknowable proposition to state that 'something cannot come from nothing' and the apologists will tend to state that it just 'makes sense' or that we lack any examples of something coming from absolute nothingness. This is an argument from ignorance. Even if we do lack any examples of something coming from nothing (which is not true), it is nonetheless possible until it is demonstrated that something, in fact, cannot come from nothing. Apologists often have no understanding that it is quite different to state that one believes something can come from nothing versus stating that the premise that something cannot come from nothing is unknowable and thus requires the premise to be rejected. It is the difference between stating 'premise x is unknowable and thus invalid' versus 'I do not believe in premise x.' It is equivalent to the statement that 'I reject belief in god claims due to a lack of evidence' versus 'I believe no gods exist,' which confound apologists for the exact same reason.
There is also the presupposition that nothingness was the initial state, of which very few modern cosmologists accept. There is certainly no evidence that nothingness ever was a state or could even be a state by definition (depending on which definition one uses, of course). Rather, the energy condensed in the singularity (which also may not have ever actually existed) may have always existed in some form or another prior to the Big Bang event. Even the phrase “prior to the Big Bang event” might be illogical as time itself, which defines what is before or after, also originates from the Big Bang, not just the contents of the universe. It seems reasonable to state that nothing could come before time itself, but we simply do not know for sure if this logical limitation represents an actual limitation.
The third premise also is a rejection of infinity, which is merely an argument from incredulity. A lack of imagination capable of accepting infinity is not a reason to reject infinity. The common sense gut feeling that makes a human wince at infinite series of causal events is no premise that has any logical power. That is a fallacy known as an appeal to common sense. And again, the conclusion is an argument from ignorance, as it takes as a unsupported fact that God is the only possible uncaused first cause. He lacked another explanation based on his own lack of imagination and the ridiculously primitive science of his age and inserted his God since no other explanation existed. Even if we had no explanations today for his premises (if his premises were assumed to be true), this still does not only point to one possible supernatural conclusion.
The Argument from Contingency
Contingent beings are caused.
Not every being can be contingent.
There must exist a being which is necessary to cause contingent beings.
This necessary being is God.
This is a tautology. It is circular. There is no way to know that a god is an uncaused or non-contingent being. This is merely a reflection of his particular faith which would proclaim, without evidence, that his god is uncaused and non-contingent. That is, his definition for his god is a presupposition. Thus the premise is flawed as it is unknown and likely unknowable. This negates the whole argument, but for completeness, the conclusion is also just another argument from ignorance as it is not the only conclusion possible. One can simply replace this non-contingent being as the immortal alien specie that engineered contingent beings on Earth. There is no evidence for either possibility.
The Argument from Perfection
Objects have properties to greater or lesser extents.
If an object has a property to a lesser extent, then there exists some other object that has the property to the maximum possible degree.
So there is an entity that has all properties to the maximum possible degree.
This being is God.
This is based on another Aristotelian concept of extent. This argument does not demonstrate how to select for which properties are being considered to lead to the god conclusion. One would have to say that 'all properties' also includes evil. Thus the god being defined has the maximum possible degree of evil. Of course the entire second premise is completely and logically false. Just because degrees of extent exist does not automatically mean some being exists that has the maximum of these degrees. If that were the case, one could say unicorns exist. It would be the horse with the maximum values of the attributes of a horse (plus a horn). Just because we can imagine a being with maximum properties does not make it possible. Finally, the conclusion can be just as easily restated as 'this being is Zeus,' or 'this being is Superman.'
The Argument from Design
Among objects that act for an end, some have minds whereas others do not.
An object that acts for an end, but does not itself have a mind, must have been created by a being that has a mind.
So there exists a being with a mind who designed all mindless objects that act for an end.
Hence that being is God.
'An object that acts for an end' is a vague concept. One might take this to mean an object with purpose or goals. This seems to work well in this argument as indeed it seems that some purposeful objects do have minds and some do not. Mindless objects with purpose or goals seems impossible unless the purpose or goals were given to these objects. But this does not mean a god had to be the individual that imbued purpose or goals on the mindless objects. Rather, purpose for life forms boils down to survival and natural selection ensures organisms with better features tend to survive. The purpose is longevity and/or stability. But this purpose is after the fact. Similarly, the Moon might seem to have the purpose of causing the tides. But the idea that something had to give the Moon that purpose is to think backwards. The moon causes tides, so we see an action caused and imbue purpose for no good reason.
It is a presupposition that the purpose was given instead of being simply a consequence of that object. If tides are necessary for life, which they very well might be, then it is not that the purpose was given to the Moon to cause tides. It is a backwards way of thinking about the anthropic principle. Human life developed on Earth. Were Earth different in certain ways, life could not have developed here. The fact that we are here does not justify us in assuming there is a purpose to the features that were compatible to our existence. If this planet were different, and life did not develop, we would have likely just developed on another planet where the conditions were right, and would have called that planet Earth instead.
The anthropic principle is a real eye-opener for people when it is first presented to them. People tend to think that the universe looks like it is just perfect for our existence which points to purpose. But that is based on our ego, our sense of importance. We would like to believe that we are so special that the whole universe is here for our benefit. The anthropic principle turns this around into a logical position independent of our ego. If our universe were much different, we might not have ever existed in this universe. That might actually be true. Despite the fact that we cannot know this to be a fact given we have but one universe to assess, and have only assessed a small fraction of it, we do know for sure that the conditions for life did occur in our universe at least in our small region thereof. But that is not to say it was designed for us. There may well be other forms of life that have evolved completely differently than ours elsewhere in this universe. In addition, there might well be more than one universe, or several configurations for universes.
Thus our universe, the one we observe, has the right configuration for life to exist, as obviously, we are here. We see a universe that is compatible for our existence because were it any different, we would not be here to ask the question in the first place. Rather, if this universe were indeed incompatible, we would be in some other universe where conditions are compatible. It does not even require an infinite number of universes. In any large sample of possible configurations, at least one would have the variables compatible for life. And we do not even know just how 'tuned' a universe would have to be to permit life. After all, 99.99999999% (more 9's than I have room for) of our universe is utterly hostile and incompatible to our type of life. So there might very well be other universes that are vastly more compatible than ours for life to exist. Here is a few examples of better universes than ours:
Universe B: An Oxygen-mix permeates space (making space suits pointless). Harmful radiation does not permeate all of space due to this intermediate atmosphere.
Universe C: Life similar to ours formed on a similar planet, but instead of having most of that planet being covered by undrinkable salt water, it is instead mostly covered by fresh water with more land than water for living land animals to populate.
Universe D: Life forms are based on completely different chemistry, or maybe no chemistry at all, just collections of energy in some other unimaginable structure). There is no need for metabolism, just the acquisition of more energy to expand the 'population'.
Any of these universe designs would be far more compatible for human existence, and they were but concepts that materialized in the brain of a human author. Surely a god would have chose a better configuration that what we have.
Similarly, if the Earth lacked a magnetosphere and ozone layer life may not have evolved very far, even if all of the other conditions were the same, due to radiation from the Sun and beyond. So a human might say the purpose of the magnetosphere is to deflect potentially deadly coronal mass ejections from the Sun. But this is a purpose we give to this feature, not one the feature has on its own. Jupiter has a far superior magnetic field, second only to the Sun in our solar system. That exact same feature lacks the same purpose because mankind did not evolve on Jupiter, but on Earth. Thus it is obvious that purpose is not intrinsic to all magnetic fields, just Earths (because we deem it purposeful).
The third premise is also unfounded. There does not necessarily have to exist a being, even if mindless objects cannot come into being without another process initiating its existence. And of course, we simply have no reason to call that which caused all mindless objects to exist with purpose a god.
The Watchmaker Analogy
There is an analogy that creationists often go to to argue for a designer. It is a false equivalency established between a complex designed object, like a watch, and the entire universe, or maybe simply a human eye. It ends up being an appeal to complexity, as it relies on a complex object having a difficult or even unknown naturalistic explanation to be valid. It also therefore boils down to an argument from incredulity and ignorance as it is of the standard form "we lack a better explanation, for x therefore god".
As the argument goes, if one were to walk down a beach and pick up a watch from the sand, it is indeed evident that somehting or someone had to design the watch. But this is only valid because it is contrasted relative to natural things, like the grains of sand, the sea, and your hand. The analogy fails for creationists as they must believe everything was designed and created. The watch they pick up is on a beach made of watches, beside a sea of watches. They only use the term watch as an analogy for complexity, and have nothing to contrast it with to determine that it is indeed designed as everything to them is designed.
A great question to ask a person who resorts to this analogy breaks down their failure to see the problem with this bad analogy. "So, to contrast, what would a non-designed eye/universe/watch look like?" They will be unable to answer this question for a few reasons. But the most important reason they will fail to offer an explanation is that they have no frame of reference for what is natural versus design as to them natural is the same as design, and of course we do not recognize design that way. We only recognize an object is designed by comparing it to other designed things, past experience of watching objects be designed and built, and contrasting them against natural processes.
Defining God Into Existence
The 'Five Ways' of Aquinas are somewhat complex versions of the simpler notion of defining a god into existence. If we were to say that energy is god, then sure, that “god” exists. But what makes it a god? What one is actually saying in this case is that energy, plus some more attributes, are god. If there are no further attributes beyond the typical natural definition, then swapping the perfectly adequate term energy for god is pointless.
This same problem applies to any other claims that are of similar structure. God is love. OK, but why not just call it love? What makes love synonymous with god or is there some additional attributes that make it more than the lesser term? One thing that tends to be the case with these statements is that the thing that the god happens to be is typically used vaguely. And when the term is something scientific, the person making the claim often lacks the capability to properly define the term. They often give really bizarre definitions for the term. In those cases they are not really saying something like 'god is energy' but instead are saying 'god is something like my weird version of what I think energy is without any reason.'
In the 'Five Ways' we see how the arguments end with 'that first cause is god' or 'that perfect being is god'. These statements are made as a matter of fact, without any evidence for the actual existence of that entity. If by some miracle a theist made a modified argument similar to one of the 'Five Ways' that lacked any contradictions, any inherent logical fallacies, or otherwise were intrinsically sound arguments, when they get to the conclusion and use a phrase like 'that first cause is god' they are right back to where they started as they have not explained the equivalence of the two terms. Their argument could only end with 'therefore there was a first cause,' such as in this case but they would be unable to make the case that the first cause is somehow a transcendent intelligent entity.
When confronted with this problem they typically resort to further statements without explanation such as 'I never posited that god was intelligent' or 'I never said god was transcendent' in which case they are still defining god into existence as most versions of modern theological gods hold that god has at least a few normal attributes.
God is typically transcendent, that is, independent of space and time or otherwise beyond our universe. This is the same as stating god is supernatural.
God is typically intelligent, though not always. The god(s) of Christianity, Islam, and Hinduism are typically thought of as thinking entities and being particularly intelligent.
What comes next is less common attributes, or ones that are at least not as well agreed. Even those who think they agree with the following attributes might actually not understand what the conditions are for these attributes. When given the definitions they often retract belief in those attributes often exposing gaping contradictions in their belief systems.
God is omnipotent. That is, god typically is regarded as having unlimited powers, capable of doing anything. Most would also maintain that this power has to be logically consistent such that god cannot create a contradictory thing out of principle like a square circle, or a rock so heavy he cannot lift it.
God is omnipresent. This means that god is typically thought as being everywhere and anywhere at the same time in all states, past present and future. This would be consistent with a transcendent being, even if that being were not an actual god. For example, a highly advanced alien race that lives in hyperspace would have this capability and attribute. This attribute usually has to be coupled with others to build up a being worthy of regarded as a god, at least in definition.
God is omniscient. This means god is all-knowing. Though most Christians believe this to be true about their god, their theology and dogma present blatant contradictions that make this impossible or inconsistent. For example, if their god knows everything, which would include any event past, present or future, then that god would have known beforehand the various situations of mankind that ended up in repeated failure (per the Bible myths), such as Eve eating the fruit. God may have given her the choice to eat or not eat, but their god would have known that Eve would eat the forbidden fruit even before that god bothered creating the planet and Eve in the first place. That god would have known beforehand that mankind would reject him, and that he would have to end up destroying the world per the Biblical flood myth. That god would know that an atheist would be born that would write these very words and would reject belief in Jesus Christ as divine, thereby ending up in hell. That god would have known in advance that Lucifer would challenge him, that he would have to create hell, that he would have to send nonbelievers there, and that this author would be one of them. It is not that people lack freedom of choice, or free will, it is that even if people exercise their free will, that god already knows which decisions they will make and thereby made a universe with the ridiculous rules that would send 80% (or more) of the non-Christian planet to eternal torment, some for simply not believing.
This is why when regarding the concept of eternal torment and the creation of hell and the rules for damnation, the ball remains in god's court as to who goes and who gets to heaven. If god wanted to, he could have created a universe where people lacked a reason to reject him (such as an utter complete lack of evidence). God could have created a better system for getting people to heaven than a contradictory book about a brutal killing of himself as a blood sacrifice to himself that nobody bothered to write about until it was so distorted and such an old story that rational people cannot regard it as factual. That god could have created a universe like heaven where one supposedly still has free will but without suffering or this weird game of believing on faith versus believing rationally with the brains that god supposedly designed that tend to regard things based on reason.
So when a Christian says their god is omniscient, one can easily explain the contradictions that create. Then they must concede that their god is not all knowing. One can even point out that their god is obviously not omnipotent, or it would have been far more logical to just create heaven and let free-willed people live there (especially since that is where believers are supposedly going to end up anyway). At this point all you have left is an omnipresent being that decided to build an ant farm that hides his own existence, where he can play games with peoples heads and create people that end up being eternally tormented.
Of course, any god that hides his existence is indistinguishable from a god that does not exist and has an equal impact on our existence of a god that does not exist.