Is reason the slave of the passions?

Well, "very few" is always in the eye of the beholder, but I'd like to challenge this a little bit. The majority is Humean, I agree with that, but there are a number of non-Humean moral philosophers about moral motivation, for example Scanlon and Shafer-Landau. It's actually an ongoing and long-standing debate and with good arguments for both sides.

The SEP article on moral motivation summarizes part of the debate.[1]

[1]: https://plato.stanford.edu/entries/moral-motivation/#HumVAnt...

> Reason is, and ought only to be the slave of the passions...

However, given the context, I suspect that the use of the word "ought" here has a slightly different meaning than we tend to infer these days.

  I will do what I will do
  And what I do shows me
  what I want to do.

  I am but an adviser to myself,
  Trusted but reluctantly.

I don't disagree with the second part. But the ought is explicit in THN, like 'n4r9 says below. I can think of two (definitely not the only two) plausible interpretations:

1. Reason is necessarily the slave of the passions. If so, there is no sensible way in which it ought be, since normative claims require that a thing could be otherwise. If Hume truly means that, then his "ought" is probably more of an admonishment against trying (and inevitably failing) to usurp the passions. This is a different sense, but I think it's close enough in kind to justify the interpretation.

2. Reason't isn't necessarily the slave of the passions. This makes the "ought" clause more intelligible from my position, but isn't really supported by Hume's account of moral action (i.e., how we find ourselves driven to it).

> This is a factual, not a normative claim.

It's normative in the context of the "admonishment" interpretation above. But yeah, not from #2.

Hume argues explicitly for free will via compatibilism. The SEP has an excellent summary of the argument[1], but in sum: what matters for moral responsibility is hypothetical liberty. Our ability to will (undisputed by Hume) grants us HL.

The interplay being passions (physically ended or otherwise) and voluntary/involuntary action in Hume's account is complex and can't be accurately reduced to a deflation of free will.

> As a side point, I've noticed that pretty much all these cutting edge, modern ideas that we believe have overthrown the ideas of the past were all around at the same time as Plato. In fact, a number of dialogues deal with debating concepts such as relativism, scientism, Nietszche's will to power, Kant's idea that we are trapped by mental constructs, etc. Intelligent design was even a big thing, and apparently was what started Socrate's on his philosophic quest.

I think this is a misapprehension of Modern (i.e., 17th to 19th century) philosophy. Modern philosophy is explicitly a rediscovery and re-evaluation of Classicial philosophy, having been largely lost to (or dogmatized within) the Western world. Overarching ideas follow suit; Hume, Kant, et al. make explicit reference to their forebears. And that's not to say that Modern philosophy lacks in innovation: there is no appreciable equivalent to Kantian duty, Millian global happiness, Cartesian skepticism, &c in Classical philosophy. Modern political theory doesn't exist without natural law, &c.

FWIW, I don't think that "scientism" is an intelligible subject within modern philosophy: it's only within contemporary philosophy that we've really begun to develop a formal account of what science actually is. Hume, Kant, and contemporaries don't have a rigorous concept of science discrete from the general practice of philosophy in the natural domain.

Similarly for Socrates and intelligent design: I'm guessing you're referring to his teleological claims. But keep in mind the historical context: the Greek religion was explicitly concerned with dividing the natural world into the domains of anthropomorphic gods, and Hesiod's Theogony was already 200+ years old by Socrates' time. Given this and his reference to pre-Socratic thought on teleology, it's unlikely that he had anything resembling contemporary creationism in mind.

> Reading through modern philosophy strikes me as pretty mundane, and it seems as if these modern philosophers were really myopic and either never read classic philosophy (most probably did) or just picked out the pieces they liked and ignored the counter arguments. Then they get paraded around as if they are brilliant innovators to an audience that doesn't know any better.

What audience? I was educated in philosophy, and I certainly wasn't taught (or primed) to treat Modern philosophers as brilliant innovators in contrast to Classical philosophers. On the contrary: both groups were held in extremely high regard, and Classical philosophy remains central to contemporary ethics (see Anscombe, Arpaly, and other revitalizers of virtue). Formal logic is introduced with Aristotle. Ontology is introduced with Plato.

In any case, it's important to not interpret the different eras of philosophy as existentially clashing with or ignoring the others. The history and development of philosophy is a unified one.

[1]: https://plato.stanford.edu/entries/hume-freewill/