St. Thomas Aquinas Five WaysThe First Way: Argument from Motion1. Our senses prove that some things are in motion.2. Things move when potential motion becomes actual motion.3. Only an actual motion can convert a potential motion into an actual motion.4. Nothing can be at once in both actuality and potentiality in the same respect (i.e., if both actual and potential, it is actual in one respect and potential in another).5. Therefore nothing can move itself.6. Therefore each thing in motion is moved by something else.7. The sequence of motion cannot extendad infinitum.8. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.The Second Way: Argument from Efficient Causes1. We perceive a series of efficient causes of things in the world.2. Nothing exists prior to itself.3. Therefore nothing is the efficient cause of itself.4. If a previous efficient cause does not exist, neither does the thing that results.5. Therefore if the first thing in a series does not exist, nothing in the series exists.6. The series of efficient causes cannot extendad infinituminto the past, for then there would be no things existing now.7. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.The Third Way: Argument from Possibility and Necessity (Reductio argument)1. We find in nature things that are possible to be and not to be, that come into being and go out of being i.e.,contingent beings.2. Assume that every being is a contingent being.3. For each contingent being, there is a time it does not exist.4. Therefore it is impossible for these always to exist.5. Therefore there could have been a time when no things existed.6. Therefore at that time there would have been nothing to bring the currently existing contingent beings into existence.7. Therefore, nothing would be in existence now.8. We have reached an absurd result from assuming that every being is a contingent being.9. Therefore not every being is a contingent being.10. Thereforesome being exists of its own necessity, and does not receive its existence from another being, but rather causes them. This all men speak of as God.The Fourth Way: Argument from Gradation of Being1. There is a gradation to be found in things: some are better or worse than others.2. Predications of degree require reference to the uttermost case (e.g., a thing is said to be hotter according as it more nearly resembles that which is hottest).3. The maximum in any genus is the cause of all in that genus.4. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.The Fifth Way: Argument from Design1. We see that natural bodies work toward some goal, and do not do so by chance.2. Most natural things lack knowledge.3. But as an arrow reaches its target because it is directed by an archer, what lacks intelligence achieves goals by being directed by something intelligence.4. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.http://web.mnstate.edu/gracyk/courses/web%20publishing/aquinasfiveways_argumentanalysis.htmAnselm: Ontological Argument for Gods ExistenceSt. Anselm, Archbishop of Cantebury (1033-1109), is the originator of the ontological argument, which he describes in theProslogiumas follows:[Even a] fool, when he hears of a being than which nothing greater can be conceived understands what he hears, and what he understands is in his understanding. And assuredly that, than which nothing greater can be conceived, cannot exist in the understanding alone. For suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater. Therefore, if that, than which nothing greater can be conceived, exists in the understanding alone, the very being, than which nothing greater can be conceived, is one, than which a greater can be conceived. But obviously this is impossible. Hence, there is no doubt that there exists a being, than which nothing greater can be conceived, and it exists both in the understanding and in reality.The argument in this difficult passage can accurately be summarized in standard form:1. It is a conceptual truth (or, so to speak, true by definition) that God is a being than which none greater can be imagined (that is, the greatest possible being that can be imagined).2. God exists as an idea in the mind.3. A being that exists as an idea in the mind and in reality is, other things being equal, greater than a being that exists only as an idea in the mind.4. Thus, if God exists only as an idea in the mind, then we can imagine something that is greater than God (that is, a greatest possible being that does exist).5. But we cannot imagine something that is greater than God (for it is a contradiction to suppose that we can imagine a being greater than the greatest possible being that can be imagined.)6. Therefore, God exists.Intuitively, one can think of the argument as being powered by two ideas. The first, expressed by Premise 2, is that we have a coherent idea of a being that instantiates all of the perfections. Otherwise put, Premise 2 asserts that we have a coherent idea of a being that instantiates every property that makes a being greater, other things being equal, than it would have been without that property (such properties are also known as great-making properties). Premise 3 asserts that existence is a perfection or great-making property.Accordingly, the very concept of a being that instantiates all the perfections implies that it exists. SupposeBis a being that instantiates all the perfections and supposeBdoesnt exist (in reality). Since Premise 3 asserts that existence is a perfection, it follows thatBlacks a perfection. But this contradicts the assumption thatBis a being that instantiates all the perfections. Thus, according to this reasoning, it follows thatBexists.Second VersionAs it turns out, there are two different versions of the ontological argument in theProsologium. The second version does not rely on the highly problematic claim that existence is a property and hence avoids many of the objections to the classic version. Here is the second version of the ontological argument as Anselm states it:God is that, than which nothing greater can be conceived. And [God] assuredly exists so truly, that it cannot be conceived not to exist. For, it is possible to conceive of a being which cannot be conceived not to exist; and this is greater than one which can be conceived not to exist. Hence, if that, than which nothing greater can be conceived, can be conceived not to exist, it is not that, than which nothing greater can be conceived. But this is an irreconcilable contradiction. There is, then, so truly a being than which nothing greater can be conceived to exist, that it cannot even be conceived not to exist; and this being thou art, O Lord, our God.This version of the argument relies on two important claims. As before, the argument includes a premise asserting that God is a being than which a greater cannot be conceived. But this version of the argument, unlike the first, does not rely on the claim that existence is a perfection; instead it relies on the claim thatnecessaryexistence is a perfection. This latter claim asserts that a being whose existence isnecessaryis greater than a being whose existence is not necessary. Otherwise put, then, the second key claim is that a being whose non-existence islogically impossibleis greater than a being whose non-existence is logically possible.More formally, the argument is this:1. By definition, God is a being than which none greater can be imagined.2. A being thatnecessarilyexists in reality is greater than a being that does notnecessarilyexist.3. Thus, by definition, if God exists as an idea in the mind but does not necessarily exist in reality, then we can imagine something that is greater than God.4. But we cannot imagine something that is greater than God.5. Thus, if God exists in the mind as an idea, then God necessarily exists in reality.6. God exists in the mind as an idea.7. Therefore, God necessarily exists in reality.This second version appears to be less vulnerable to Kantian criticisms than the first. To begin with, necessary existence, unlike mere existence, seems clearly to be a property. Notice, for example, that the claim thatxnecessarily exists entails a number of claims that attribute particular properties tox. For example, ifxnecessarily exists, then its existence does not depend on the existence of any being (unlike contingent human beings whose existence depends, at the very least, on the existence of their parents). And this seems to entail thatxhas the reason for its existence in its own nature. But these latter claims clearly attribute particular properties tox.And only a claim that attributes a particular property can entail claims that attribute particular properties. While the claim thatxexists clearly entails thatxhas at least one property, this does not help. We cannot soundly infer any claims that attributeparticularproperties toxfrom either the claim thatxexists or the claim thatxhas at least one property; indeed, the claim thatxhas at least one property no more expresses a particular property than the claim thatxexists. This distinguishes the claim thatxexists from the claim thatxnecessarily exists and hence seems to imply that the latter, and only the latter, expresses a property.Moreover, one can plausibly argue that necessary existence is a great-making property. To say that a being necessarily exists is to say that it exists eternally in every logically possible world; such a being is not just, so to speak, indestructible in this world, but indestructible in every logically possible world and this does seem, at first blush, to be a great-making property. As Malcolm puts the point:If a housewife has a set of extremely fragile dishes, then as dishes, they are inferior to those of another set like them in all respects except that they are not fragile. Those of the first set are dependent for their continued existence on gentle handling; those of the second set are not. There is a definite connection between the notions of dependency and inferiority, and independence and superiority. To say that something which was dependent on nothing whatever was superior to anything that was dependent on any way upon anything is quite in keeping with the everyday use of the terms superior and greater.Nevertheless, the matter is not so clear as Malcolm believes. It might be the case that, other things being equal, a set of dishes that is indestructible in this world is greater than a set of dishes that is not indestructible in this world. But it is very hard to see how transworld indestructibility adds anything to the greatness of a set of dishes that is indestructible in this world. From our perspective, there is simply nothing to be gained by adding transworld indestructibility to a set of dishes that is actually indestructible. There is simply nothing that a set of dishes that is indestructible in every possible world can doin this worldthat cant be done by a set of dishes that is indestructible in this world but not in every other world.And the same seems to be true of God. Suppose that an omniscient, omnipotent, omnibenevolent, eternal (and hence, so to speak, indestructible), personal God exists in this world but not in some other worlds. It is very hard to make sense of the claim that such a God is deficient in some relevant respect. Gods indestructibility in this world means that God exists eternally in all logically possible worlds that resemble this one in certain salient respects. It is simply unclear how existence in these other worlds that bear no resemblance to this one would make God greater and hence more worthy of worship. From our perspective, necessary existence adds nothing in value to eternal existence. If this is correct, then Anselms second version of the argument also fails.

http://www.iep.utm.edu/ont-arg/