What does "reason is, and ought only to be the slave of the passions" mean?

It means to not to go overboard with philosophy. Not to over think everything.

It sounds like another way of saying “go with your gut feeling.”

Throw out the “and ought only to be” And you get the sentence: “Reason is the slave of the passions.” What does that means to you?
To me that sentence means we don’t think clearly when passionate about something.
He obviously was not an engineer. Do not drive over any bridge he designed!

I guess he is saying keep your head in the heat of the passions. Reason perseveres over passion. Nice ideal, but it ain’t me. When I get wild screw reason.

@Adirondackwannabe He’s actually saying the exact opposite. That’s where the “ought only to be” comes in.

Hume is purposefully exaggerating to make his point about the sentiments being the ultimate reason that we do anything. He does not mean that reason is incapable of leading to action. He does mean that reason alone is incapable of leading to action. So it’s not that reason and emotion are opposed to one another, but rather that reason relies on emotion.

Think about it this way: reason is really good for doing means-end reasoning, but where do you get the ends? If I tell you that you need to do A to get result B and that you need to do C to get result D, you can’t figure out whether you should do A or C until you figure out whether you want result B or result D.

To put this in more practical terms, let’s say I offer you the contents of Box A or Box B. Presumably, you’ll want to know what’s in them before choosing. That’s because the logical choice is to pick the one containing whatever you want more. But wanting is a feeling. It is the input your reasoning needs to figure out what sort of output is most appropriate (that is, choosing Box A or Box B).

The same thing, according to Hume, applies to ethics. When you watch someone do something terrible, you can’t find the badness of their action in any scientific description of their action. The description of a blade cutting open skin is the same in the case of a murder as it is in the case of a life-saving surgery. How we feel about the various cases—about the motivations for the actions and their consequences—is important in figuring out whether they are right and wrong.

This isn’t to say that the matter is wildly subjective, however. How we feel is grounded in human nature (which is more or less universal) and tempered by what Hume calls “the general point of view” (because we have to abstract from our own biases to judge a case fairly). Nevertheless, reason can never make a judgment without the input of reason. And so, reason is the slave of the passions (it’s just the way things are) and ought to be the slave of the passions (giving it more of a role would lead us astray).

Interesting note: a lot of contemporary work in psychology and neuroscience suggests that Hume is completely right with regard to his claims about human nature and how moral and practical reasoning work.

^ The “Mechanical Properties of Prestressed Self-consolidating Concrete” is so much easier to study and understand…

@LuckyGuy Yeah, science and engineering are pretty easy when it comes right down to it. You get a lot more data to work with and a whole history of results to draw on as presuppositions. But it also involves a lot more math right upfront—which is why there are so many English majors. ~

Plenty of philosophy majors are trying to avoid math, too. But then they find out about symbolic logic.

Here’s a life philosophy for you. I call it the conservation of grief principle. The basic premise to contribute to society by making the world better while minimizing grief.

There is a sliding scale with a measurable ratio that determines where we fit. Let me start off with an example Imagine a hitchhiker needing a ride. If I pick him up it would take me 2 minutes out of my way. but it would save him 10 minutes of walking. That is a 5 to 1 grief reduction ratio. Sure, I’ll give him the ride. But what if it takes me 1 minute and saves him one minute – a grief reduction ratio, GRR = 1? Do I still do it? Nope. That is below my threshold. Let him walk. A sociopath will inflict a lot of grief without helping someone A very high GRR infinitely high. At the pother end of the scale is someone like Mother Theresa who will reduce grief and devote her entire life to it. Her GRR threshold is near 0.
Imagine a Conservative CEO for a large company demanding a salary in the 9 figure region while objecting to a minimum wage increase. His GRR might be well into the 1000’s . Someone willing to donate time and money to work in a soup kitchen helping the homeless might be in the low single digits.

If you accept living at a GRR of 1 or lower, you are giving up much of your life to helping and pleasing others at the expense of yourself. You can potentially burn out. If you live at high GRR levels you give and do nothing for others and thus deserve to rot in your bathroom alone after suffering a fatal heart attack while sitting on the toilet.
The world would be a better place if we all strived to be somewhere in between.

I figure I am, in aggregate, about a GRR 3–5. I will donate generously to a cause if I see the users will work to better conditions sustainably – like teaching a man to fish. If I am asked to just give a fish thatt will eaten on the spot with no change in conditions, I usually refuse. I favor causes like Habitat for Humanity while refusing to hand over money when it will be consumed with no visible long term improvement. .
I will gladly pick up a hitchhiker at a GRR of 5. I will gladly go 10 minutes out of my way if I have the time and it saves them over 50 minutes.
I will gladly spend time teaching someone how to do a task but will not do the task myself.
Yep. GRR 3–5 sounds about right.

Does that count as a philosophy?

Engineers… Sheesh.

To Hume has been attributed the statement, “You can’t derive ought from is” Whether or not Hume ever said those exact words, it is a good summary of his attitude. You can’t determine what you should do from just observing the world and thinking about it. There must at root be some driving passion and sense of rightness that guides our actions. You can come up with guidelines, like @LuckyGuy, but in the end there is always going to be some degree of subjectivity in weighing alternatives.

It is quite simple but quite deep and I think true though it runs counter to what we generally believe even two centuries after Hume’s day. Reason isn’t there at the beginning it steps in later to advise how best to achieve what we already want or how we can justify what we have already decided to do.

@LuckyGuy “Does that count as a philosophy?”

It sure does! It looks like a form of utilitarianism—the most mathematical of all the ethical theories, of course!—sometimes called negative utilitarianism (because it is focused on removing or minimizing the things that make us unhappy rather than increasing or maximizing the things that make us happy). And despite its critics, I think you are in pretty good company holding such a view.

I read it to be encouragement to not let our passions override our reason.