I often wonder how a person who is trained in philosophy can be so utterly confused about logic. It's not that they don't know the rules of logic, such as modus ponens, or that they are unable to apply those rules in a syllogism. It doesn't take an education in philosophy to be able to construct an argument that follows the rules of logic. Even an animal can reason something like this: If I can unlatch the door, then I can escape. But it does take a deeper level of understanding to be able to formally state what those logical rules are, and express them in symbolic terms. The animal does not know that he us using modus ponens, despite the fact that he actually is using it in his primitive reasoning process. But there are philosophers who don't see the distinction between using logic and thinking about logic.
If a dog reasons as described above, he is using logic, but it may be simple logic that doesn't involve complex sequences of steps to arrive at the conclusion. Various animals have been shown to employ logical reasoning at different levels of complexity. Only humans have the mental capacity to perform highly complex sequences of logical operations. The difference between man and other animals is just a matter of degree. It's not that we are the only creature capable of performing logic, but we do have a greater capacity for complexity. And along with that, we have the ability to think in metalogical terms. That is, we can think about logic itself, and make symbolic representations of our logical processes. But that's not equivalent to employing logic in our reasoning.
Logic is natural. It is part of our physical world. Who would suppose that our thinking dog would not be able to escape by unlatching the door if people had devised different rules of logic, thus rendering his modus ponens invalid? The dog doesn't know or care how we humans formulate the rules of logic. It is physical reality that guides his reasoning process. It is no different from any other physical laws. The dog knows that if you throw a ball in the air, he can catch it when it comes back down, and he can even predict where it will come down. He doesn't know the first thing about Newton's laws, but he sees and feels the effects of those laws, and he knows that when you throw something up, it will come back down, following the path of an arc. The laws of physics are part of nature, whether or not we have distilled them into formulas. In the same vein, the laws of logic are part of nature, and that would still be true if Aristotle had never lived. And just as a dog can predict the path of a ball, he can perform logical reasoning to some degree.
That's why computers can perform logical functions, too. The individual logical steps are physical functions. No programmer ever instructs computer how to do modus ponens, or any other basic operation, such as logical conjunction. A device as simple as a transistor performs those operations inherently - because they are physical functions. It's so simple, even a brain can do it. But Victor Reppert would have us believe otherwise:
If a brain is literally what a brain is supposed to be on physicalism, a bunch of particles, then it is NOT up to modus ponens. Different parts do different steps, so what makes it modus ponens? If something provides a perspective, then, sure, even a computer can do modus ponens. But only considered as an extension of the mental states of its programmers, and only as a product of intelligent design.. - ReppertVictor is confused. What the programmer does is supply the antecedent and the consequent to the logical operation. The computer naturally knows how to perform the operation itself. The programmer also instructs the computer on what sequence of operations to perform, and in that sense, the reasoning process is an extension of the mental states of the programmer. But to say "it is NOT up to modus ponens" is categorically wrong. The performance of simple logical operations is mechanical.
Human intelligence does bring something additional into the process. It is the assignment of meaning to the operands of the function. When we say If A then B, the truth of logic holds, no matter what A or B represent. For an electronic device (say two transistors configured as tandem inverters), the label A might be attached to the input, and B might be the output. Asserting the input causes the output to be asserted. The device performs its logical function flawlessly, but it doesn't know what meaning its human operator might attach to the labels A and B. A mechanical device simply performs logical functions according to the laws of physics.
That's not to say that the assignment of meaning must necessarily be a God-given non-material facility. Living creatures have additional properties (beyond the fundamental laws of mechanics) that give them capabilities beyond those of simple machines. Emergent properties are a reality of nature. No atom can steer to the right or left, but when atoms are assembled into a car, the car has the capability of steering. While Victor insists that these emergent properties of living things (and especially humans) are not the product of any natural evolutionary process, the fact is that they all have natural explanations:
1. First person perspective.
If there is consciousness, there is a first-person perspective. It is just the perspective of the entity that is conscious (whatever that entity may be), with regard to itself. Whether consciousness is natural or supernatural makes no difference. If consciousness can arise by any means (evidence indicates that it evolved naturally), and the conscious being can contemplate both itself and other things, then logically, there MUST BE a first-person perspective, as well as a second- or third-person perspective. Victor's reasoning here is quite sloppy.
Purpose is inherent in all living things. It is an emergent property of certain assemblages of particles that have the function of metabolism. That function is sustained in part by physical mechanisms that allow the organism to sense and obtain the material resources to perform its metabolic processes. A bacterium mindlessly finds and consumes food. If the organism has a complex brain, it can be aware of a sense of purpose, and it has the cognitive ability to plan its actions with the goal of fulfilling that purpose. In addition, the basic sense of purpose can be extended to "enhanced survival", which is striving toward goals that are consistent with the creature's interests but not necessarily for immediate survival. Human brains often add confusion to this sense of purpose by postulating that it comes from God.
"Aboutness", the supposed connection between a thinking entity and things that are external to it or that don't even exist, is really nothing more than connections between neurons in the brain. All concepts of external and non-existent things are configurations of some part of the brain. I see a tree, and that configures some set of neurons in my brain as a "concept". When I think about the tree, I am invoking that conception, which is entirely inside my brain. This is the basis of meaning. If you see symbols A and B on a piece of paper, the brain may make an associative neural connection between its concept of the symbol and some other concept (like A = Joe), thus assigning meaning to the symbol.
In this case, Victor is correct about the physicalist view. We do things because of the state of the physical world, not because it is our duty. It is an extension of the concept of purpose. Even though it may not appear so at first glance, we do what is in the interest of perpetuating our genome, and that usually translates to what is in the interest of the individual. Evolution has programmed us to behave in an altruistic way, and comply with cultural norms of behavior, because that is a survival strategy that has been successful. The concept of "duty", especially duty to God, is just a theistic idea that rationalizes and possibly attempts to regulate human behavior.
5. The "thinghood" of the brain.
We humans have a propensity to classify things to simplify the way we think about them. Brains are indeed a bunch of particles, in the much same way that a car is nothing more than a collection of atoms - but not just any collection of atoms. They have to be assembled in a particular way to have the functionality that we attribute to a car. And all such collections having similar functionality are classified in our minds as "cars". Likewise, not just any collection of particles will have the functionality of a brain. The "thing" that we call a brain is a particular (and extremely complex) assemblage of particles having the functionality of controlling the processes and activities of a biological creature. And the fact that we humans call it a brain doesn't change anything about the physical reality. It is still a bunch of particles. And once again, this is not an argument against naturalism.
Getting back to the topic of logic, we can see that there is nothing supernatural about the existence of logic itself. It is just as natural as the laws of physics, but it does take a thinking mind to comprehend the existence of those laws. And while theists try hard to justify their belief in the supernatural essence of mind with all kinds of arguments that attempt to show it can't be physical, those arguments fall flat. You have to simply ignore the cognitive sciences. You have to ignore the evidence of evolution of creatures with increasing cognitive function. You have to be oblivious to the whole world of science and scientific facts if you want to go on thinking that mind can't possibly be physical. And to put a cap on it, hang on to the ridiculous notion that logic itself is immaterial, and can only be the product of a divine mind. To cling to such ignorance in today's world requires willful denial of science and any scientific-based understanding of reality.
How logical is that?