Most of the arguments for God’s existence start with observations of the natural world, concluding a posteriori, after the fact, that God’s existence is the most probable explanation of those observations.  As such, most arguments for God’s existence are inductive and so are subject to the problem of induction; even when these arguments are strong, they do not provide proof but only a high degree of probability. Their conclusions are always falsifiable if and when observations are found to be flawed or incomplete (and the premises of the argument thus shown to be untrue), as well as if and when a more probable explanation of these observations is suggested.  Because of the limitations of arguments for God’s existence that start with observations, St Anselm sought to demonstrate God’s existence from reason alone.  In his Monologion (1075-6) he proposed a deductive argument based on the grades of perfection in things, arguing that the existence of God as supreme perfection is contained within claims that other things are more or less perfect.  Nevertheless, Anselm’s argument was criticized by his predecessor as abbot of Bec, Lanfranc.  Lanfranc argued that Anselm had not succeeded in demonstrating God’s existence from reason alone, because the premises in his argument depended on observations, even though they did contain his conclusion.  Because of Lanfranc’s criticism, Anselm determined to try to demonstrate God’s existence from reason alone in the Prosologion (1078).  Anselm developed two novel a priori arguments in this work and he remained confident of his own success, despite criticisms leveled during his lifetime, writing…

“I BELIEVE that I have shown by an argument which is not weak, but sufficiently cogent, that in my former book I proved the real existence of a being than which a greater cannot be conceived; and I believe that this argument cannot be invalidated by the validity of any objection. For so great force does the signification of this reasoning contain in itself, that this being which is the subject of discussion, is of necessity, from the very fact that it is understood or conceived, proved also to exist in reality, and to be whatever we should believe of the divine substance.” Concluding words of Anselm’s “Responsio” to Gaunilo

Nevertheless, history has shown that St Anselm did not succeed in demonstrating God’s existence from reason alone. 

In the Prosologion Book II St Anselm presents a simple version of what Kant later termed an Ontological Argument from God’s existence.  He started by quoting Psalm 14:1 and claiming that atheists are fools because they accept that God is “that than which nothing greater conceived of” and claim that there is nothing by that definition that exists in reality, when existence is a perfection and so my definition a property of “that than which nothing greater can be conceived of”.  For St. Anselm, if God only existed in the mind, it would always be possible to conceive of something greater, namely something that existed in reality, so existence in reality must be a property of God.  This argument was criticised by Gaunilo of Marmoutiers in his wittily titled “On behalf of the fool.” Gaunilo objected to St. Anselm’s claim that Atheists accept his definition of God as “that than which nothing greater can be conceived of.” He argued that people can recognise a word without forming an idea of what it refers to in their minds and that is particularly likely in the case of God, because it is a word which refers to something that is unlike any other thing and which is beyond most peoples’ experience.  Further, Gaunilo argued that it is possible to have in one’s minds all sorts of ideas of things which do not exist in reality.  He then used St Anselm’s own example of a painter and a painting to reason that the idea of something in the mind must always precede understanding that that idea also exists in reality.   St Anselm rejected Gaunilo’s points in his Responsio, arguing that if Atheists do indeed recognise the word God but not have any idea what it refers to then so much more are they fools!  Later, Descartes’ examples of triangles and valleys support St Anselm’s reasoning here – how could somebody claim to recognise the word triangle without understanding its essential predicate of three-sidedness?  St Anselm then reasoned that God is not like the idea of a unicorn or a Gruffalo, because unlike any other imaginary thing, the idea of God is of a being whose supreme nature logically contains existence in reality.  He hit back at Gaunilo, claiming he never intended his example of the painter and painting to be used in the way that Gaunilo used it.  Nevertheless and despite these responses, Gaunilo’s criticisms are effective.  Having ideas “in intellectu” for words to refer to depends on experience, on having ideas about similar things to draw on.  When an artist paints, they form an idea of what they want to paint in their minds that usually draws on experience before they then apply paint to the canvas and come to understand their painting as an object that now exists in reality as well as in the mind.  When an artist paints a triangle, they have experience of three-sided shapes to draw on and if not that, then some experience of shapes full stop.  However, if an Artist tried to paint God, they would have no comparable experience to draw on at all, so the idea of God in the artist’s mind would always be prior to and separate from the idea of God existing in reality.  Atheists have no experience of God and so the word “God” is just a sound, a sign without anything to point towards.  Later, St Thomas Aquinas agreed with Gaunilo.  While he accepted that God’s existence can be said to be self-evident and known through reason alone to somebody who really understands all that can possibly be known about the nature of God, Aquinas noted that in practice most people have little concept of what God is.  In Summa 1,2,1 Aquinas wrote: “Now because we do not know the essence of God, the proposition is not self-evident to us; but needs to be demonstrated by things that are more known to us…— namely, by effects.”  In this way, St Anselm failed to demonstrate that Atheists are fools because God’s existence can be known from reason alone.

Further, a version of St Anselm’s argument in Proslogion II presented by Descartes was later criticised by Immanuel Kant and Bertrand Russell.  Persuasively, Kant pointed out that St Anselm and Descartes are wrong to claim that existence is a perfection.  Taking the example of a job interview, a candidate who exists is not more perfect than a candidate who does not, rather the application of the non-existent candidate is meaningless.  Superficially, it might seem that Kant is nitpicking.  A real chocolate cake, any real chocolate cake, will always be greater, more perfect, more tasty etc. than any imaginary chocolate cake, even an imaginary one with zero calories.  No less authorities than St Anselm and Descartes saw this as a matter of common sense.  Despite this, Kant’s point deserves deeper consideration.  In logic, following Aristotle, there are two kinds of predicates – accidental predicates and essential predicates.  Accidental predicates are properties that an object may or may not have – like cherries or cream in the case of a chocolate cake.  Essential predicates are properties that an object must have or not be that object – like chocolate-flavour in the case of a chocolate cake.  In the Critique of Pure Reason (1781) Kant argues that existence is neither an essential predicate of anything, nor really an accidental predicate.  Focusing for the moment on existence as an accidental predicate, existence cannot be seen as a quality that an object might or might not have in the same way that cherries or cream are qualities that a chocolate cake might or not have.  To explain this point, Bertrand Russell used the example of a claim such as “the present King of France is bald” – it seems like a meaningful claim and capable of being true or false, but in fact because there is no present king of France the claim is meaningless.  St Anselm implies that there is a scale of perfection, the idea of an imaginary God appearing lower down the scale, with Gods having more or less perfect attributes appearing alongside, with the real God at the top of the scale.  In fact real existence is a precondition of appearing on the scale and being capable of comparison.  Russell points out that when St Anselm defines God as “that than which nothing greater can be conceived of” he begs the question and smuggles the existence of God as the object into the premises of his argument, reasoning that existence must de dicto be an accidental predicate of God.  If there is no “that than which nothing greater can be conceived of” then predicating anything of it is meaningless.  St Anselm needs to establish the existence of God before his demonstration of God’s existence will work, so the argument could only ever succeed for a person who had reason to believe already, on other grounds.  For these reasons as well, St Anselm failed to demonstrate God’s existence from reason alone.

Perhaps aware of the shortcomings of his argument in Proslogion Book II, in the Proslogion Book III St Anselm had already presented a different type of Ontological Argument, reasoning that it is greater to exist necessarily than only contingently, so necessary existence is a property of God as “that than which nothing greater can be conceived of.”  Here, St Anselm is arguing that existence is not just an accidental predicate of “that than which nothing greater can be conceived of” but is actually an essential predicate of God, to use Descartes’ later example as three-sidedness is an essential predicate of being a triangle.  In his “On behalf of the fool” Gaunilo criticised this argument as well, trying to reduce it to absurdity by using the analogy of a perfect island.  Nobody but a fool would believe that an island exists simply because somebody says that it is a perfect island, so existence (necessary or otherwise) must be predicated of it.  In this last criticism, at least as applied to the argument presented in Proslogion III, Gaunilo fails to show that Anselm’s argument is flawed.  As St Anselm wrote in the Responsio:

“I promise confidently that if any man shall devise anything existing either in reality or in concept alone (except that than which a greater be conceived) to which he can adapt the sequence of my reasoning, I will discover that thing, and will give him his lost island, not to be lost again.”

St Anselm is right to remind Gaunilo that necessary existence cannot logically be said to be a property of islands, unicorns or gruffalos for that matter.  Such things exist within time and space, contingently.  No contingent existence can necessarily exist.  Only God, who is “that than which nothing greater can be conceived of” has and must by definition have the unique property of necessary existence.  Despite this, however, St Anselm assumes that the idea of necessary existence is possible.  Persuasively, Immanuel Kant argued that because all our possible knowledge is of contingently existing things, any claims about necessary existence are like a “cupola of judgement”.  For Kant, all existential claims must be synthetic, capable of being verified through sense-observations.  We simply cannot claim to know that anything necessarily exists, so St Anselm’s argument is speculative and must fail to demonstrate God’s existence from reason alone.  Further, Kant argues that existence cannot be an essential predicate of anything.  He wrote:

“If, then, I try to conceive a being, as the highest reality (without any defect), the question still remains, whether it exists or not. For though in my concept there may be wanting nothing of the possible real content of a thing in general, something is wanting in its relation to my whole state of thinking, namely, that the knowledge of that object should be possible a posteriori also…”

Kant is effectively agreeing with Gaunilo, although supporting his argument rather better, in reasoning that existence is “out there” in the world of the senses and so incapable of being demonstrated analytically, through reason alone, and without reference to the senses.  Today, the vast majority of people would side with Kant and Gaunilo in their understanding of what it means to exist, and for this reason St Anselm failed to demonstrate God’s necessary existence from reason alone.

Nevertheless, after WWII Kant’s world-view started to be questioned and along with it his claims that all existential statements have to be synthetic and that existence cannot be an essential predicate of anything.  Perhaps drawing on those like Hegel who drew attention to cracks in the foundations of Kant’s critical philosophy early in the 19^th Century, scholars such as Hartshorne and Quine pointed out how dogmatic Kant’s understanding of existence and meaning was.  For Hartshorne, Kant’s criticism of seeing existence as an accidental predicate is fair, but ignores the possibility that necessary existence could be an essential predicate of God and only God.  Hartshorne reasoned that either God’s existence is contingent (which it cannot be, by definition), or God’s existence is necessary and necessary existence is impossible or God’s existence is necessary and possible, in which case God exists.  Rejecting Kant’s limited world-view, Hartshorne argued that God’s necessary existence is not impossible, so God necessarily exists.  Of course, Hartshorne’s argument depends on his ability to reject the claim that necessary existence is an impossible concept.  JN Findlay strongly disagreed with Hartshorne on this point, arguing that by showing that God’s existence can’t be contingent and can only be necessary when necessary existence is impossible,

“it was indeed an ill day for Anselm when he hit upon his famous proof. For on that day he not only laid bare something that is of the essence of an adequate religious object, but also something that entails its necessary non-existence…’ [First published in Mind, April 1948] 

While others have agreed with and built on Hartshorne’s reasoning, including Norman Malcolm and later Alvin Plantinga, those who side with Hartshorne tend to be those who believe in God on other grounds.  Again, attempts to revive the Ontological Argument serve to show that Anselm failed to demonstrate the existence of God from reason alone to anybody who doesn’t already believe in God on other grounds.

In conclusion, St. Anselm’s arguments in the Proslogion fail to demonstrate the existence of God from reason alone.  Gaunilo, Kant and Russell among many other critics have shown how St. Anselm’s reasoning is problematic, firstly by showing how Atheists need not accept the first premise of the argument, that “God is that than which nothing greater can be conceived of” and by undermining the whole attempt to demonstrate existence by analysing the concept of anything, and then by showing that existence is not a perfection or quality that can properly be accidentally predicated of anything and that necessary existence is impossible, because existence cannot be an essential predicate of anything.  That is not to say that St Anselm’s arguments have no value.  While they fail to demonstrate God’s existence from reason alone, for those who already believe in God – or at least for those who already reject Kant’s critical world view with its limitation on possible knowledge and meaningful claims – the arguments remain an important part of articulating their faith and revealing the nature of God.