Reddit mentions of Grounding for the Metaphysics of Morals: with On a Supposed Right to Lie because of Philanthropic Concerns (Hackett Classics)

I think you will learn the most by reading five textbooks, such as A History of Philosophy, volumes 1, 2, 3, 4, and 5; or something like Metaphysics: The Fundamentals, The Fundamentals of Ethics, Theory and Reality: An Introduction to the Philosophy of Science, An Introduction to the Philosophy of Religion, and An Introduction to Political Philosophy.

If what you have in mind is more of a "Great Books" program to get your feet wet with some classic works that are not too difficult, you could do a lot worse than:

• Plato's Euthyphro, Apology, Crito, and Phaedo, often published together under the title The Trial and Death of Socrates. Socrates is so important that we lump together all Greek philosophers before him as "the Presocratics," and this cycle of dialogues is a great window on who he was and what he is famous for.
  
• The Basic Works of Aristotle. "The philosopher of common sense" is not a particularly easy read. Cicero compared his writing style to "a flowing river of gold," but all the works he prepared for publication are gone, and what we have is an unauthorised collection of lecture notes written in a terse, cramped style that admits of multiple interpretations. Even so, one can find in Aristotle a very attractive system of metaphysics and ethics which played a major role in the history of philosophy, and holds up well even today.
  
• René Descartes, Discourse on the Method and Meditations on First Philosophy. Descartes is called the father of modern philosophy, not so much because modern philosophers have widely followed his particular positions (they haven't) but because he set the agenda, in a way, with his introduction of methodological scepticism.
  
• David Hume, An Enquiry Concerning Human Understanding. I think Elizabeth Anscombe had it right in judging Hume a "mere brilliant sophist", in that his arguments are ultimately flawed, but there is great insight to be derived from teasing out why they are wrong.
  
• If I can cheat just a little more, I will lump together three short, important treatises on ethics: Immanuel Kant's Grounding for the Metaphysics of Morals, John Stuart Mill's Utilitarianism, and Anscombe's paper "Modern Moral Philosophy".

The book I always recommend people start out with is Sophie's World, not because it's the most in-depth, but because it's the most accessible for a newcomer. It's also the most entertaining I've read. If you want something more in-depth, Russell's History of Western Philosophy is generally this subreddit's big recommendation, although I personally wouldn't say it's a great starting point. His reading of some thinkers is not great, and he's not quite as good at dumbing down certain ideas to an introductory level.

A good summary of philosophy will help you for a couple reasons. One, it will give you enough information to find out what thinkers and ideas interest you. If you're interested in a particular question or thinker, then that's obviously where you should go. Philosophy of religion? Logic? Aesthetics and art? Language? There's plenty written on all these topics, but it can be a bit overwhelming to try and just attack all of philosophy at once. Like any other field, there will be parts of it that click with you, and parts that don't really seem all that appealing. Find your niche, and pursue it. In addition to giving you an idea of where to go, a good overview will put ideas in context. Understanding Augustine and Aquinas will make more sense if you know that they're working with a foundation of the Greek thought of Plato and Aristotle. Descartes wrote his meditations during the enlightenment, and was a major contributor to much of the emphasis on reason that defined that era. Nietzsche and Kierkegaard's existentialist ideas become more powerful when you realize they're critiquing and challenging the technicality of Kant and Hegel. Ideas don't exist in a vacuum, and while you can't be expected to know all the details of everything, your niche area of interest will make more sense if you understand it's context.

As for easier texts that I'd recommend trying out (once you find an area of interest), here's a few that are pretty important and also fairly accessible. These are texts that are generally read by all philosophy students, due to their importance, but if you're just into this for personal interest, you can pick and choose a bit. Still, these are important works, so they'll be very good to read anyways.

Plato - Apology: not terribly dense, but an accessible text in which Socrates basically defends his pursuing philosophical thought. I'd recommend this as an accessible introduction that will get you to feel like philosophy matters; think of it as pump-up music before a big game.

Plato - The Republic: this is arguably Plato's most important work. In it, he talks about the nature of men, politics, education and art.

Aristotle - Nichomachean Ethics: a text that deals with leading a life in accordance with virtue. Aristotle's style is a bit dry and technical, but he's also very important.

Augustine - On Free Choice of the Will: a dialogue similar to Plato's in which Augustine argues that the existence of God does not conflict with man having free will.

Aquinas - Selected Excerpts: he wrote a lot, so you don't wanna try reading a whole one of his works. This selects his key ideas and puts them in bite-sized chunks. He's a big Christian thinker, arguing for the existence and goodness of God and related theological concepts.

Descartes - Meditations on First Philosophy: Descartes uses reason to prove he exists, along with some other things. Pretty easy to read, although it sparked a revolution in thought, making epistemology a central problem of philosophy.

Kant - Grounding for Metaphysics of Morals: one of his easier works, but it's still one of the more technical works I'm recommending, in which Kant demonstrates that morals are a priori.

Kierkegaard - Fear and Trembling: one of my favorite books, Kierkegaard writes about the nature of faith using the story of Abraham and Isaac as his starting point. A huge critic of Kant's obsession with pure reason, he is generally considered to be the first existential thinker.

Nietzsche - Beyond Good & Evil: Nietzsche is one of the more controversial thinkers in history. Also a critic of Kant, he is one of the most profound critics of religion. This book is one of his more important, in which he talks about his problems of religion, the culture around him, and at times points us in the direction he wants us to go. Know that he doesn't write in a terribly direct manner, so if you choose to read him, come here for assistance. He's a bit different to read, and can be challenging if you're not ready.

This list is by no means exhaustive, and having a good reference to help you along will be very helpful.

At least for Anarchists or other left-libertarians it should also be important to actually read up on some basic or even fundamental ethical texts given most political views and arguments are fundamentally rooted in morality (unless you're a orthodox Marxist or Monarchist). I'm sadly not familiar enough with applied ethics to link collections of arguments for specific ethical problems, but it's very important to know what broad system you're using to evaluate what's right or wrong to not contradict yourself.

At least a few very old texts will also be available for free somewhere on the internet like The Anarchist Library.

Some good intro books:

• The Fundamentals of Ethics by Russ Shafer-Landau
  
• The Elements of Moral Philosophy by James and Stuart Rachels
  
• Ethics: A Very Short Introduction by Simon Blackburn
  
  Some foundational texts and contemporary authors of every main view within normative ethics:
  
  
• Nicomachean Ethics by Aristotles for Classic Virtue-Ethics. Martha Nussbaum would be a contemporary left-wing Virtue-Ethicist who has used Marx account of alienation to argue for Global Justice.
  
• Grounding for the Metaphysics of Morals by Immanuel (or Emmanuel) Kant for Classic Deontology. Kantianism is a popular system to argue for anti-statism I believe even though Kant himself was a classical liberal. Christine Korsgaard would be an example of a contemporary Kantian.
  
• The Methods of Ethics by Henry Sidgwick for Classic Utilitarianism. People usually recommend Utilitarianism by John Stuart Mill, but most contemporary Ethicists believe his arguments for Utilitarianism suck. 2 other important writers have been R. M. Hare and G. E. Moore with very unique deviations from classic Utilitarianism. A contemporary writer would be Peter Singer. Utilitarianism is sometimes seemingly leading people away from Socialism, but this isn't necessarily the case.
  
• Between Facts and Norms and other works by the contemporary Critical Theorist Jürgen Habermas may be particularly interesting to Neo-Marxists.
  
• A Theory of Justice by John Rawls. I know Rawls is a famous liberal, but his work can still be interpreted to support further left Ideologies. In his later works like Justice as Fairness: A Restatement you can see him tending closer to Democratic Socialism.
  
• Thus Spoke Zarathustra by Friedrich Nietzsche for... Nietzsche's very odd type of Egoism. His ethical work was especially influential to Anarchists such as Max Stirner, Emma Goldman or Murray Bookchin and also Accelerationists like Jean Baudrillard.
  
• In case you think moralism and ethics is just bourgeois propaganda maybe read something on subjectivism like Ethics: Inventing Right and Wrong by J. L. Mackie
  
• Or if you want to hear a strong defense of objective morality read Moral Realism: A Defense by Russ Shafer-Landau orc

That was a happy coincidence haha, if you want more details on deontology and this whole universalization principle, Kants Grounding for the metaphysics of morals is a great book.(Dont know if amazon links are allowed but: http://www.amazon.com/Grounding-Metaphysics-Morals-Supposed-Philanthropic/dp/087220166X )