Reason leads us to God

This page last updated January 26th, 2023

This page in brief ….

We can test different worldviews, such as naturalism and theism, by seeing how well they can explain the world we experience. On this page I examine our human ability to reason and think logically even about abstract concepts.

If the world is composed of physical things (matter and energy), which is the most common conclusion of naturalists and atheists, how could natural selection have produced brains that are both free and capable of thinking rationally? For if our brains are only physical, then they are only capable of acting according physical cause-effect processes. But logic requires us to use ground-consequence thinking that starts with some facts (ground) and reasons to a conclusion (consequence).

Computers are able to use merely physical (electrical) processes to produce logical results, but they have been designed to do so. So I examine how evolution could have produced a similar result. It would require our physically-determined brain processes to be able to produce logical outcomes.

We can see that animals have evolved to respond to threats and opportunities in their environment, but does this constitute thought, or just a survival reaction? It would seem that the best survival strategy is to flee when there is even a small risk of a predator, which would mean that their brains evolved in response to risk rather than truth.

It is hard to see how higher thought would evolve in this way. And even harder to see how we humans could discuss matters if our brains were merely programmed to produce logical results rather than actually doing logic.

There are many aspects to this question, far more than I can read, let alone write about here. But it seems that our ability to reason is something that physicalist naturalism has great difficulty explaining. It seems that either theism (belief in a creator God) or a non-physicalist naturalism (whatever exactly that may be) are better explanations.

I finish with a list of references for further reading.

Two world views

Two basic ideas try to explain the world we experience. Naturalism is the view that there is no supernatural – no gods, no non-physical beings or non-physical forces. Naturalists are logically atheists.

Commonly, naturalists believe the universe is composed only of the physical or material things we are familiar with – matter and energy. The terms physicalism or materialism refer to this view. Less commonly, a naturalist may believe that there are non-physical things – for example, David Chalmers suggests we view consciousness as a fundamental property of the universe, a non-physicalist version of naturalism.

In contrast, those who believe that God, or gods, or non-physical beings exist may be called supernaturalists.

Which view describes the world we experience?

One of the ways atheists and theists each try to show their conclusion is true is to start with observable features of our world, and try to show that these are compatible with the belief we ourselves hold, but incompatible with the opposite belief.

On this page I examine our brains and our ability to reason, features of our common human experience that may offer clues to the existence or otherwise of God.

We experience our brains as having the ability to think of abstract concepts and reason our way to a conclusion, despite being the product of evolution and random natural selection. How can we explain this?

Our first response is likely to be that random processes cannot produce logical reasoning, a doubt shared by Charles Darwin, who said: “With me the horrid doubt always arises whether the convictions of man’s mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy”.

So, is physicalism left with this dilemma, or is there a satisfactory explanation? Let’s examine the question in detail.

Cause and effect

If the world is only physical, then only physical events can cause other physical events. And physical events are governed, or described, by laws that are generally well understood.

(Random events may also occur by chance, but these have no cause and are no help in explaining rational thought.)

This means the electrical and chemical processes in our brains are described and controlled by physical laws. And those processes, if materialism is true, are all there is to you and to me, as Francis Crick said. There is no mind, no “us”, apart from the processes.

So it seems that atheism and physicalism lead logically to the conclusion that our thoughts are determined by physical laws, and we actually have no freedom to choose differently. In philosophical terms, we don’t have libertarian free will.

It seems that most thoughtful atheists therefore don’t believe we have libertarian free will. Famous biologist Francis Crick said that humans, including our supposedly free will, “are in fact no more than the behaviour of a vast assembly of nerve cells and their associated molecules”. Other atheists like philosopher Daniel Dennett and neuroscientist Sam Harris support this conclusion.

In contrast, if the world and human beings are more than physical, there may be non-physical processes at work, and we may be able to exercise choice outside the limitations of physical laws.

Logic and brain processes

If the physical is all there is, our brain processes, and therefore our thinking, are physical. That is, causes lead to effects according to physical laws. A neuron passes information across a synapse to another neuron, which responds in a way determined by the laws of physics. This cause-effect processing is the basis of all our thinking. And our thinking is determined by these processes.

However logic is based on ground-consequence relationships. Our beliefs are made up of every opinion we hold, and if a belief is rational, it is a consequence of the assumptions or premises we start with; and the premises are the grounds of the conclusions. For example, I hear that a politician has a certain policy (ground) so I form the belief I will vote for him (consequence). An atheist might see the suffering in the world (ground) and so form the belief that no God exists (consequence).

So to think logically, we have to be able to “see” that a consequence logically follows from the grounds we began with, and then be free to choose our beliefs accordingly.

This straightaway raises a problem for the atheist, for if physicalism is true, our brains work by determined cause-effect processes while logic requires ground-consequence processes and choice. The two are different. So at first glance, it might appear that our brains cannot do logic at all if determinism and atheism are true.

In contrast, if there is more to our thinking than physical processes, then it may be possible for us to do ground-consequence reasoning.

How can cause-effect brains do ground-consequence logic?

Since our brains are the result of evolution and natural selection, the obvious answer to this question is that natural selection has “taught” our brain’s cause-effect processes to produce ground-consequence logic. Daniel Dennett says of our brains: “syntactic engines can be designed to track truth, and this is just what evolution has done.”

For example, a computer is programmed so that its physically determined electrical processes can produce logical outcomes. So, it is argued, natural selection can lead to physically-determined brain processes producing logical outcomes just like a computer can do. Of course the human brain is more complex than a computer, and a computer doesn’t, as far as we know, have any beliefs. And (for the atheist at least) the brain isn’t designed by a designer. But the analogy offers some hope of resolving this dilemma.

We need to be clear what is being claimed here.


  1. Brain state S1 leads by physical laws at work in the brain to state S2.
  2. Each state has an associated mental state, M1 and M2.
  3. M1 does not produce M2, because M2 is produced via the physical cause and effect processes between S1 and S2.
  4. But, it is claimed, if natural selection has done its work, the brain has evolved so that M1 logically leads to M2 even though M2 isn’t the result of logic.

Thus, like a computer, the brain has come to a logical conclusion even though it hasn’t used logic, just physical laws.

Can natural selection do this?

A computer can use cause-effect electrical processes to produce logical outcomes because the hardware and software were designed to achieve this. But an atheist doesn’t believe that human brain processes were designed with an end in mind, it was all natural selection.

So how might it work?

We know that natural selection favours capabilities that increase the likelihood of reproducing. Zebras that run fast live longer than slow zebras, on average, and so are likely to reproduce more zebras with genes that enable fast running. In this way the whole zebra population becomes faster.

So for natural selection to produce a brain where cause-effect processes are capable of producing logical outcomes, that result has to lead to a greater probability of reproducing.

We can see that some cognitive faculties help animals and people survive to reproduce. A zebra that reacts more quickly when a lion appears, or a suspicious sound is heard in long grass, will be more likely to survive to reproduce than one which reacts slowly.

But it doesn’t really matter whether the zebra believes that a lion is there. What matters for natural selection is that the zebra reacts quickly and lives to breed and pass on its genes. So it doesn’t require that the zebra reasons logically that a lion is there – stopping to reason would likely make the zebra less likely to survive.

If physicalism is true, “what is required for survival is effective response to the environment, not accurate knowledge of that environment” (Victor Reppert).

Survival strategy

So the best survival strategy will likely be to react on suspicion rather than take the risk of waiting until being sure. This will inevitably lead to reacting often when the belief is false, not just when it is true.

Many of our most important survival mechanisms don’t require any reasoning and don’t produce any beliefs – for example, all our unconscious bodily processes related to breathing, regulating our bodily temperature, etc. And others work just fine with false beliefs.

So natural selection works on our reactions and actions, and, if physicalism is true, our reasoning processes and beliefs are simply by-products of natural selection. Our cognitive faculties have been selected for their ability to survive (e.g to respond to risk) rather than reason logically. Our reasoning may often be true, but often it may not. So there is no reason to think our cognitive faculties are reliable.

In contrast, if our thought processes are more than physical, we can learn from our mistakes and choose to make changes in how we think. And so mental state M1 may be capable of producing mental state M2 after all.

But don’t beliefs affect behaviour?

If materialism is true, beliefs are the result of brain states, not their causes, as shown in the diagram. Thus, if physicalism is true, it seems beliefs cannot directly influence behaviour.

But perhaps the naturalist has a resolution of this impasse. Our brains receive inputs from the external world and respond to them, so it seems likely that beliefs can likewise have an impact on brain processes, by being part of the data which our brains use to make decisions.

But it is important to note that there is no choice in this, if physicalism is true. The brain deals with these beliefs in a way determined by evolution. The beliefs have been developed in response to survival and risk reduction. They may be true or not, but the brain will only recognise this if natural selection creates, as a by-product, a brain able to discern true and false. But is this possible?

Does logic assist survival and reproduction?

It seems plausible that being able to reason assists in survival and reproduction. So wouldn’t the ability to reason accurately develop and improve via natural selection?

There are many different levels of cognitive faculties.

  • Some bacteria and amoeba are able to respond to their external environment and move to a more favourable location, but they can do little else.
  • The small parrots in my backyard have learned to perch on our doorknob and call, and we will replenish their seed, but I don’t suppose they could add 4 + 4.
  • A child of 9 can do that simple addition but probably cannot recognise Modus Ponens or calculate Bayes Theorem.
  • Once in the long distant past I gained a Distinction in a university statistics exam, but I have no idea how anyone could prove Fermat’s Last Theorem. However just over 20 years ago Andrew Wiles solved the Theorem, the proof taking 129 pages. But I doubt there are many people in the entire world who could understand it!
So can natural selection be sufficient to explain higher cognition?

As we have seen, appropriate reactions are certainly necessary for survival. So the lower end of the scale of cognitive faculties can surely be explained by natural selection. And an ability to organise and choose between competing options might well make life more efficient. But as we go higher up the scale, surely the survival and reproduction benefits reduce and the impact of other factors becomes more important.

So natural selection seems likely to favour quick, precautionary reactions, not slower analytical thinking.

Intuitive and analytical thinking

For example, psychologists sometimes classify thinking as either intuitive and analytical. The latter is more likely to employ logic, but isn’t always the most effective mode of thinking. In complex situations, or where a quick decision is required, intuitive thinking is generally more effective. An early homo sapiens who stopped to analyse the situation may not survive so well in Africa!

Sexual attraction

It is a sad but apparently often true fact that many women prefer a handsome, muscled Adonis to a clever logician, and many men are more attracted to a pretty face than to a PhD in economics. Of course, some people are both clever and attractive, but it is often not that way. Nerds like me are often not attractive to women! So clever cognitive faculties may not lead to great reproductive success.

Energy efficiency

Higher cognition puts an additional load on the human system

  • larger energy requirements,
  • a longer time between conception and full independence, and
  • a longer time to problem solve.

These are negatives for natural selection which any advantages of cognition have to overcome.

From basic to higher thought?

And while a tool-making ape may well eat better and so live and reproduce better than one without that ability, it is hard to see how the ability to program a computer or prove Fermat’s Last Theorem are going to help much in passing on genes.

Of course it may be that the ability to do higher mathematics or logic is just the same ability as tool-making. But if so, we might ask where are the mathematical geniuses among apes? There seems to be a gap, in the type of thinking as well as the depth of thinking, between practical tool-making and survival skills and theoretical and abstract thinking.

So higher levels of cognition seem unlikely to supply any significant competitive advantage, and are likely to be outcompeted by other characteristics like speed and quick reactions (to flee predators), or strength and charisma (to fight off competing males, attract mates and so reproduce more).

It seems unlikely, at least, that we can explain higher thought by physicalism and natural selection alone.

Show me a model

I have discussed this with atheists and done a little reading, and so far I have seen assertions that higher cognition can arise via natural selection. But I haven’t yet seen anyone explain exactly how it would happen, and some philosophers who argue that it cannot.

Until then, I think it is reasonable to doubt natural selection can lead to higher, more theoretical, cognition, and to await some more complete explanation.

In contrast, a human mind created by a reasoning, personal God, could easily have these abilities that we observe.

The problem of argumentation

But suppose that determinism is true and natural selection did indeed produce human brains. There are still, I think, negative implications here for atheism and physicalism.

The problem arises when people disagree. A disagreement means that our respective brains have used our determined cause-effect processes to arrive at different conclusions. Sometimes we can resolve these matters – for example, there is some piece of information that one person lacks, and when it is explained, the two former protagonists agree.

But sometimes two people can have the same information and yet still disagree – for example, questions of politics, the ethics of abortion or warfare, or the existence of God.

In contrast, if we had choice, and if our brains could do ground-consequence reasoning, we could argue the matter out, testing each other’s assumptions, arguments and conclusions. We may not reach agreement, but we may at least expose some weaknesses in each others’ arguments and give each other food for thought.

But if physicalism is true, then our brains don’t do ground-consequence reasoning, and our ability to do logic depends on how well our brain’s determined cause-effect processes can simulate logic. So if I disagree with you, it will be because my brain’s cause-effect processes don’t simulate ground-consequence reasoning in quite the same way as yours. And because our brain processes are determined, neither of us have any choice about this.

So if physicalism is true, argumentation may be useless, because it isn’t possible to change our brains’ programming. Sometimes it does feel like this when we argue with someone of a resolutely different opinion (think current politics). Nevertheless we all still discuss and argue for our viewpoint.

In contrast, supernaturalism allows us to argue with some hope that change is possible.

A computer example

We have seen that a computer can be used as an analogy for a brain (if physicalism is true). Both work by determined cause-effect processes which have been programmed to simulate ground-consequence logic (the computer is programmed deliberately by a programmer, whereas the brain has been programmed by natural selection). So let us imagine two computers programmed by different programmers communicating with each other.

It turns out that the two computers are given the same instructions but produce different results because of their different programming. They can try to argue which result is right, but they have different bases for their conclusions – they have been programmed differently – and each sees their conclusion as correct and the other’s as erroneous.

The computers are at an impasse. There is nothing they can do to resolve it. They have no ability to choose beyond the programming in their brains (CPUs). The only way this impasse can be resolved is for the programmers to step in and each check the logic of their programs.

A depressing conclusion

I am suggesting that, if physicalism is true, it is the same for brains. We can argue, and sometimes we will be able to convince the other person. But on more complex matters which require nuanced judgment, if physicalism is true, there is no basis on which to show one view is more right than the other, and no ability to change. Our brains were programmed by natural selection, and won’t easily be changed.

Of course our brains do change as a result of new inputs. But that change, like all other thoughts, isn’t because we see the logic (if physicalism is true) but because that is how the physical processes in our brains have been programmed by natural selection.

It isn’t a palatable conclusion, for it seems to render philosophical argument futile.

So when I ask the question on this blog, Is there a God?, and an atheist argues with my conclusion, they are assuming something about discussion and logic and truth that may be difficult to justify from their viewpoint.

It is little wonder that philosopher Thomas Nagel describes the naturalist explanation of rational thought as “laughably inadequate” while John Searle wrote:

In order to engage in rational decision making we have to presuppose free will.

Where do we go from here?

I think most of us feel that this can’t be the truth. We really are able to think, evaluate and choose based on the merits of the argument. We get it wrong sometimes, sometimes our biases trip us up, and sometimes we try to address issues at the limit of our cognitive abilities (like I am doing here!). But overall, our conversations can be sensible and worthwhile.

Even if our logic tells us that our thinking is determined by physical laws, not logic, we will go on discussing and arguing. Our actions will speak louder than our beliefs.

How does a naturalist respond to this dilemma?

I have experienced three different responses.

1. There’s no problem

These ideas seem to me to show that, arguably, physicalism, and hence atheism, are not compatible with the world we experience and the way we arrive at conclusions. This is a reason to consider physicalism and atheism untrue. There are other reasons for and against belief in God, of course, but this is one argument that should be considered.

But some atheists shrug all this off. They don’t see any problem, it doesn’t concern them, and they don’t seem to have any answer.

I think this is a response they would criticise if a theist wasn’t interested in answering an atheist argument like the problem of evil. So I feel it isn’t adequate.

2. A misunderstanding of determinism

I have found many atheists have what seem to be inconsistent views about determinism and free will. When the nature of physicalism is explained, they accept that our “choices” must be determined. But then they describe how they make choices in ways that suggest genuine freedom to choose (i.e. libertarian free will). I feel they are showing in their own reactions the dilemma for naturalists – their philosophy tells them they can’t have free will, but their experience tells them they do.

I think the problem is compounded by compatibilists, who argue that free will can be compatible with determinism, but it is a truncated form of free will that doesn’t allow any real choice between alternatives. Compatibilism sometimes seems to be clever words to allow naturalists and determinists to use freewill language while re-defining free will so it isn’t really free.

3. Explanations

Of course thoughtful naturalists have considered all these matters. Some (e.g. Thomas Nagel and David Chalmers) argue that physicalism isn’t true. There are non-physical but non-supernatural realities, for example consciousness. But this seems to me to be an unrealised hope rather than something that that can be seen and assessed.

But most naturalists remain physicalists. They argue that natural selection can do the job and has produced brains that can reason well enough. But the arguments I have seen (and been able to understand) seem to fall short of what is required to rescue physicalism from severe doubt:

  • All physicalist answers struggle to explain the fundamental difficulty of how beliefs can be adaptive simply because they are true. Too often they remain assertions rather than explanations.
  • The explanations I have seen seem to be relevant to very basic cognition that directly leads to survival, but not to higher more theoretical reasoning that seems to confer no survival advantage and has some significant disadvantages. So how would higher levels of thought ever evolve, if physicalism is true?

So I haven’t seen any convincing detailed discussion of how true beliefs can be consistently produced by merely physical processes, and how it might work out in discussion among people with different viewpoints on complex questions. So the significant doubt remains.

Most of us know that we are capable of reasoning accurately even about complex theoretical matters, and physicalism has not, in my opinion, been able to explain this. In contrast, supernaturalism has a ready explanation for our cognitive abilities – that they were created by a reasoning God.


  1. Physicalism has not (as far as I can see) provided a satisfactory explanation for higher, theoretical reasoning. If physicalism was true, our reasoning would be determined by physical laws, not by logic. Our ability to reason would be unreliable and inconsistent. We wouldn’t believe things because they were true, but because natural selection had given us brains that concluded they were true, whether they were or not.
  2. Supernaturalism doesn’t have the same difficulties. Reasoning is quite consistent with creation by God.
  3. This argument therefore throws considerable doubt on physicalism. It increases the probability that physicalism is not true and hence that God exists. Reasoning is an unresolved challenge to physicalism and atheism.
  4. Theism isn’t the only alternative to physicalism. A non-physical form of naturalism may be true. But I haven’t yet seen anything specific to give any reason to accept this conclusion.
  5. This matter is way too complicated to discuss fully here, or to be easily understood. If you want to read further, the references below may help.

Read more

My discussion here is brief, and I claim no philosophical expertise. These are live issues between philosophers like Alvin Plantinga, JP Moreland and Victor Reppert, on one side, and John Searle, Daniel Dennett, Jerry Fodor, Ruth Millikan and Michael Draper on the other side. I have read writings by all of these, but nowhere near comprehensively. Understanding many of them is a stretch! My sources include:

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