George Johnson (In the Palaces of Memory: How We Build the Worlds Inside Our Heads, 1991) expressed it best: "As neuroscience comes closer to explaining more about the brain and mind, some scientists, and even a few philosophers, are wondering if philosophy itself could be approaching its denouement." (p. 209.) In other words, philosophy is merely the outcome of human personality (highly deterministic but open to discipline): "What personality type are you?" C.G. Jung (Psychological Types, 1923) understood this early on with his "four types of mind" and from this some 256 "flavors" or varieties of human personality. If each "type" is color coded (as in some contemporary discussions on the 'difficult personality'), we have a mighty pyramid: Red (sensorial: "know-it-alls" [some leaders; some criminals] 47% of human personality; Green (the "relators": 33% of all human "types"; Blue (the "thinkers" or brooders: 16% of the world population; and Yellow: the "intuitors" 4% of all personality "types." Patricia Churchland was the first to explore this in her book Neurophilosophy (1986). She is resigned to the possibility that neuroscience will someday replace philosophy. Philosophy will be no more. Thus, the same dumb questions asked again and again will cease; and we will be free to go on to better ground.
First this conflates the whole of philosophy with rational psychology, and second, psychology, conducted at the level of detail of neuroscience would be totally intractable.
Let me address the second issue first. We keep the field of biology, despite knowing that physiology and genetic competition are really all about chemistry. In fact we create an extra field, biochemistry, out of the small area where this fact is most relevant. Why? Well, most of chemistry has nothing to do with biology, and the level of detail at which chemistry actually predicts biology is simply not usable or informative. We need to get the larger issues out of the way of biochemists on both extremes for them to have any hope of comprehending the tasks put to them.
But the bigger issue is that a map is not its territory. Assume we had a perfect psychology that encompassed not just the neurology, but all of the appropriate epiphenomena including language, logic, all the influences on decision-making processes, the personality structures that create all forms of bias or interpretation, their formation, and their interaction with those of other humans and with data.
This total understanding of the functioning of the brain would not solve the basic issues of philosopher any more than our current knowledge of anatomy and histology address the basic needs of an athlete. OK, so physiology study gives us a model of how the body works, and it is a good model. How does that come into practice? How much does it even matter, except when there are basic problems like injuries or equipment adaptations that can be fixed in its terms? That is the same degree to which neurology matters to philosophy. Not much.
The purpose of philosophy is primarily about "When do I use what kinds of ideas for what purposes. How do I address uncharted territories of thinking?" More parallel to the athlete's issues: "When do I best use what anatomy to what purposes? How do I address new physical situations and challenges as they arise?" than anything a neurologist could answer: "How does thinking happen?" as an anatomist might answer "How do flexion, tension and leverage happen?"
Looking at how generations of philosophers have addressed the same 'dumb' questions is like watching now players since the dawn of football have addressed the same repetitive process of using the field and positions to their best advantage. The point is not really answering those questions -- in fact we might be sad when parts of philosophy drift off into 'real sciences' like computing. It is about having ways of answering questions, that feed the rest of science. The same way soccer is not just about winning games, and we may be sad to see a good game end. It is about having ways of winning games, that inform other parts of life.
"Science says the first word on everything, and the last word on nothing." - Victor Hugo
Neuroscience may eventually replace or redefine large portions of what was historically referred to as the philosophy of mind, since questions about the internal workings of e.g. consciousness, memory, language, reasoning and similar phenomena are inherently scientific.
However, not all philosophy is philosophy of mind, and ultimately neuroscience and philosophy have a different purpose - one cannot be thought of as replaceable by the other. Neuroscience aims to provide falsifiable and verifiable answers about the nervous system. Philosophy, on the other hand, doesn't seek to solve scientific problems, but primarily to redefine questions and interpret answers. Science can provide insight and describe various phenomena at a certain level of abstraction, but some questions require a philosophical context. For example, consider the problem of the morality of slavery. A neuroscientific perspective may describe various cognitive, cellular and psychological effects occurring in the enslaved individuals, but what else? You've got raw data and knowledge, but how can you act on it without a philosophical context? In contrast, a philosophical approach could argue about the immorality of slavery without needing the scientific insight in the first place.
I like jobermark's argument, so I will not repeat it but take it further. It reminds me of a Richard Feynman quote, which we could paraphrase: neuroscience is as useful to philosophers as ornithology is to birds.
Neurological facts do not help to address pressing philosophical concerns, in the same way that knowledge about other species of birds will not help the robin catch his worm. An awareness of other animals is definitely beneficial to all birds, since recognizing other species gives an evolutionary advantage to predators as well as their prey. However, this is not the same as ornithology, and has nothing in particular to do with being a bird. In the same way, neuroscience is largely orthogonal to philosophy in the sense of being a philosopher or philosophizing. Knowing is not doing, and no amount of neuroscience alone will help you settle on the best moral system or determine why there is something rather than nothing.
Some questions will be addressed and "solved". Knowledge about how we think, the constraints and rules imposed by our neurological makeup, that is truly formidable insight. Yes, it will probably put to rest some questions about consciousness and free will. No one doubts it, and it would be silly to not use the new knowledge for the purposes of philosophy. But in my mind that is a positive development, as it will purify philosophy and distill the really important questions. Neuroscience will extend philosophy and take it to new levels rather than replace it.
Neuroscience will not replace philosophy. Indeed, it will not even be very helpful for understanding psychology. Neuroscience is roughly about the structural and chemical properties of your brain. However, your brain is a universal classical computer: it can compute anything that any other computer can compute. Such a computer can be made up of multiple types of units on the lowest level. For example, both Friedman and Toffoli gates (two different types of three bit gates) are universal for classical computation. And there are many other gates or sets of gates that are universal. As a result the actual lowest level operations don't make much difference to what your brain can do once it is capable of doing and of composing some very simple operations.
This has many consequences that are fatal to the idea of replacing philosophy with neuroscience. For example, there is no particular reason to think that a particular idea is encoded in the brains of everyone in the same way. As such there is no particular reason to think that a detailed description of what is happening in the brain of one person with a particular idea will correspond to what is going on in the brain of another person with the same idea.
It gets worse. The vast bulk of what people are doing refers to stuff that is outside their brains. For example, astrophysicists are trying to understand black holes and stuff like that. So to understand the brain of an astrophysicist working on black holes you would have to understand black holes and how to investigate them. And that is largely a matter of physics and philosophy of science, not neuroscience. Note that neuroscience has no bearing on philosophy of science since that is largely about what scientists ought to do not what they happen to do in reality. For example, if a scientist makes a mistake while doing a calculation we should be interested in how to fix the mistake and avoid such mistakes in the future. Even if we could read his thoughts with a brain scan there is no reason to think that this would help since what matters is figuring out the right way to do the calculation and how that differs from how he did it in reality.
There is another reason to be very sceptical about how important neuroscience will be. In order to read something you have to guess about what it means and subject those guesses to criticism until you understand it. So if a neuroscientist tried to read an idea he didn't understand from somebody's brain he would be in the same position as anybody else as far as understanding it is concerned. And since the stuff that is in the person's brain and not written down anywhere has not been considered carefully and criticised, it will not be "written" in such a way as to be easy to understand. A neuroscientist who wanted to understand some philosophical issue would be better of asking questions and having critical discussions rather than looking at patterns of brain activity.
Claiming that philosophy will be replaced by studying the brain is about as plausible as saying that the study of literature will be replaced by the study of ink and paper.
Neuroscience has the potential to answer robustly many questions that have been asked by philosophers--questions about the nature of perception, consciousness, intuitive morality, and so on. It calls into doubt assumptions that once seemed safe (e.g. internal non-contradiction) and makes solid ideas that did not originally find much favor among philosophers (e.g. mind is implemented by brain).
If it actually will give robust answers in all these areas is not yet clear, but in the areas it's already made inroads we can, post hoc, observe that, actually, philosophy was not equipped with the tools to answer the questions that were originally asked under its sphere. There are profound non-intuitive empirical "truths" that we could only reasonably have hoped to obtain via experiment, not introspection, appeal to intuition or logic, or other methods commonly employed in philosophy.
But even if neuroscience is outrageously successful (which is in doubt as it is an outrageously hard problem), there will be plenty left to do in philosophy. To give one example (to add to the others already in answers here), even supposing that neuroscience and related disciplines give a comprehensive account of intuitive morality, it doesn't fashion for us a system of ethics or tell us how to negotiate all the difficulties of defining a universal scoring system for consequentialism (or tell us which framework to use instead).
Classic philosophical questions include (but are not exclusive to) the following:
- What is the fundamental nature of consciousness?
- What is the fundamental nature of the universe?
- What is the reason of my individual existence?
- What is the reason of our existence as a species?
- How can we achieve individual happiness?
- How can we achieve the greatest happiness for the greatest number of people?
- Why is there life?
- Why is there anything at all?
While some of these questions can be addressed by neuroscience, others need to be addressed by biology, physics, mathematics or other fields of science.
While I would argue that philosophy has been rendered obselete by the scientific method as way to answer these questions and that any philosophical question can not only be addressed by science but that scientific answers will be the most reliable answers, it is not neuroscience that supersedes philosophy but rather an integrated scientific model based on the integrated data and theories from all sciences combined.
So no single scientific field can replace philosophy, but science as a whole can replace it and IMO should replace it.
What about ethics?
Science both teach us a lot about how our actions influence our happiness and stability. Herein, neuropsychology typically focuses on individual behavior, whereas sociology focuses on the collective components components and biology focuses on genetic components of our behavior.
Combined, neuropsychology, sociology and biology give a rather complete picture of human behavior and human consciousness. It allows us to model human nature in a consistent way, which in turn allows us to develop a rational moral foundation based this model.
Adding to that, mathematical studies like game theory can help us determine the impact of our actions and assess that impact with greater clarity.
The astrophysicist Arthur Eddington wrote on the contiguousness of man with nature the following:
'I am convinced that you have minds which think. Here then is a world fact to be investigated. The physicist brings his tools and commences systematic exploration. All that he discovers is a collection of atoms and electrons and fields of force arranged in space and time, apparently similar to those found in inorganic objects. He may trace other physical characteristics, energy, temperature, entropy. None of these is identical with thought. He might set down thought as an illusion-some perverse interpretation of the interplay of the physical entities that he has found. Or, if he sees the folly of calling the most undoubted element of our experience an illusion, he will have to face the tremendous question: How can this collection of ordinary atoms be a thinking machine? But what knowledge have we of the nature of atoms which renders it at all incongruous that they should constitute a thinking object?
....But now we realise that science has nothing to say as to the intrinsic nature of the atom. The physical atom is, like everything else in physics, a schedule of pointer readings.
....matter is something that Mr. X knows. Let us see how it goes: This is the potential that was derived from the interval that was measured by the scale that was made from the matter that Mr. X knows. What is Mr. X?...physics is not at all anxious to pursue the question: What is Mr. X? It is not disposed to admit that its elaborate structure of a physical universe is "The House that Mr. X Built."
....From its own point of view, physics is entirely justified. That matter, in some indirect way, comes within the purview of Mr. X's mind is not a fact of any utility for a theoretical scheme of physics. We cannot embody it in a differential equation. It is ignored, and the physical properties of matter and other entities are expressed by their linkages in the cycle. And you can see how by the ingenious device of the cycle physics secures for itself a self-contained domain for study with no loose ends projecting into the unknown. All other physical definitions have the same kind of interlocking. Electric force is defined as something which causes motion of an electric charge; an electric charge is something that exerts something that produces motion of something that exerts something that produces...ad infinitum.'
Neuroscience can answer 'how' it works but still cannot answer "Who am I?"