What should I read? Should I read the books philosophers themselves wrote or the ones that is written by someone else??? I don't want books that only give introduction. I read lots of easy introduction books and history of philosophy books and podcasts. I want something more challenging.
I would say, don't be afraid to read the major texts by the principal philosophers themselves. One of the reasons the great philosophers are considered great is that they are worth reading. That said, some are hard to understand.
Some of the greats of the 'modern' era are Spinoza's Ethics, David Hume's A Treatise on Human Nature, and Kant's Critique of Pure Reason, and Critique of Practical Reason.
My own interest is mainly in 20th/21st century philosophy in the analytical tradition. Some of the principal works in this tradition are:
- L. Wittgenstein, Tractatus Logico-Philosophicus
- L. Wittgenstein, Philosophical Investigations
- W.V. Quine, Word and Object
- W.V. Quine, The Roots of Reference
- J.L. Austin, How To Do Things with Words
- G. Ryle, The Concept of Mind
- P.F. Strawson, Individuals
- P.F. Strawson, The Bounds of Sense
- Elizabeth Anscombe, Intention
- Saul Kripke, Naming and Necessity
- Derek Parfit, Reasons and Persons
- Michael Dummett, The Logical Basis of Metaphysics
- T. Williamson, The Philosophy of Philosophy
- T. Williamson, Modal Logic as Metaphysics
If you are more interested in continental philosophy, existentialism, or philosophy outside the western traditions, others will have to provide some recommendations.
To speak with philosopher Paul K. Feyerabend: Anything goes! He was referring to the methodogy used in acquiring scientific knowledge. He was a philosopher of the sciences who seek a theory of everything of the workings of the sciences. A variety of methodologies are offered. In his book "Against Method" (which appeared in three different editions) he argued that in practice there is no methodology seen ar all. Enforcing such a methodology will surely arrest progress. Feyerabend wrote more books. "Science in a Free Society", "Farewell to Reason", "The Tyranny of Science", "Conquest of Abundance", and his autobiography "Killing Time" amongst them.
The actual practices in science are discussed by Ian Hacking, Andrew Pickering (Constructing Quarks), or Hans Radder (The Material Realization of the Sciences), to name a few.
Of course it depends on the kind of philosophy you want to know about. For the philosophy of the sciences the writers I mentioned are fully-blown. There is no philosophy for beginners in the way you ask. There is not such one in the sense of an introductionary text for quantum mechanics. You get it all fully develloped. Some words are difficult but you can look these up. The books are generally written in a very understandable language *which can't be said for the writers who advocate a methodilogy of science...).