Here is Peter Hacker's take:
We must challenge the thought that philosophy aims to contribute to human knowledge of the world. Its task is to resolve philosophical problems. The characteristic feature of philosophical problems is their non-empirical, a priori character: no scientific experiment can settle the question of whether the mind is the brain, what the meaning of a word is, whether human beings are responsible for their deeds (have free will), whether trees falling on uninhabited desert islands make any noise, what makes necessary truths necessary. All these, and many hundreds more, are conceptual questions. They are not questions about concepts (philosophy is not a science of concepts). But they are questions that are to be answered, resolved or dissolved by careful scrutiny of the concepts involved. The only way to scrutinize concepts is to examine the use of the words that express them. Conceptual investigations are investigations into what makes sense and what does not. And, of course, questions of sense antecede questions of empirical truth – for if something makes no sense, it can be neither true nor false. It is just nonsense – not silly, but rather: it transgresses the bounds of sense. Philosophy patrols the borders between sense and nonsense; science determines what is empirically true and what is empirically false. What falsehood is for science, nonsense is for philosophy.
Let me give you a simple example or two: When psychologists and cognitive scientists say that it is your brain that thinks, then, rather than nodding your head and saying ‘How interesting! What an important discovery!’, you should pause to wonder what this means. What, you might then ask, is a thoughtful brain, and what is a thoughtless one? Can my brain concentrate on what I am doing – or does it just concentrate on what it is doing? Does my brain hold political opinions? Is it, as Gilbert and Sullivan might ask, a little Conservative or a little Liberal? Can it be opinionated? or narrow minded? – What on earth would an opinionated and narrow-minded brain be? Just ask yourself: if it is your brain that thinks, how does your brain tell you what it thinks? And can you disagree with it? And if you do, how do you tell it that it is mistaken – that what it thinks is false? And can your brain understand what you say to it? Can it speak English? – If you continue this line of questions you will come to realise that the very idea that the brain thinks makes no sense. But, of course, to show why it makes no sense requires a great deal more work.