Well, I think the first thing to realize is philosophy is an art, not a science. It is, by definition, an eternally open subject. Some people love this, some people hate it. Most of the “big ideas” were fleshed out by the early Greek philosophers but have been refined and re-explored many times, particularly by the medieval Scholastics (DesCartes, Aquinas, et. al.)
So, philosophy is really a grab-bag of big questions and “big ideas”, most of which have no definite answer. Is the Universe infinite in extent and age? Believe it or not, science really has not settled this question… it’s just taken to be settled within the standard cosmology which itself is full of holes. Is matter comprised of discrete point “atoms”, or is it a continuum “wave”? QM is supposed to say that it’s “both” but it turns out that is a misrepresentation of the facts. And so on. These millenia-old questions are actually still open because the fact is they are foundational.
I would commend the Internet Encyclopedia of Philosophy to your attention. There is also the SEP. This guy is engaging, I highly recommend Epicurus to your attention, as well as just explore around on YouTube… there are tons of videos uploaded on all the old philosophers. Learning a little about the lives of the ancient philosphers is useful because the human brain is a social brain… it’s easier to retain and operate on ideas that you can place in the context of the thoughts and ideas of real human beings.
Also, as just a matter of sheer amazing insightfulness, I recommend Mises’s Ultimate Foundation of Economic Science and the first 150 pages or so of Human Action. While he doesn’t directly deal with the foundations of philosophy itself, he makes many remarks - almost offhand - that go a long ways to dispel common philosophical tarpits. A wise man will heed the philosophical insights of Mises.
If I could say only one thing to save you time and effort, it is to always remember that all aspects of learning and study are human. That includes natural philosophy (today called “science”). All studies serve human ends. And they are performed by human beings. Anything that anyone has ever thought is, in principle, comprehensible by you, too. So, beware of imbuing philosophy with a kind of theological “apartness”. Many people fall into this trap. Philosophy will not get you greater certainty regarding what is true and right. That certainty has to come from within and is a matter of maturity, not book study. In fact, I think that is what attracts people to the ancient philosophers… they were “blue sky” thinkers… their thinking was unclouded by thousands of years of prior written dogma. They didn’t need to preface every remark with 10,000 qualifications and gotchas.
Clayton -