I essentially agree with you that science can’t bridge the is-ought gap (see caveats) but it’s a good deal more complicated than the arguments you give here allow for (they are a good intro but I felt it’s worth pointing out the complexities).
When someone claims to have bridged the is-ought gap they aren’t usually claiming to have analytically identified (i.e. identified as a matter of definition) ought with some is statements. That’ s a crazily high bar and modern philosophers (and Sam Harris was trained as a philosopher) tend to feel true analytic identities are rare but are not the only kind of necessary truths. For instance, the fact that “water is H20” is widely regarded as a necessary truth that isn’t analytic (do a search if you want an explanation) and there are any number of other philosophical arguments that are seen as establishing necessary truths which don’t amount to the definitional relationship you demand.
I think the standard Harris is using is much weaker even than that.
You insist that to be an ought it must be motivating for the subject. This is a matter of some debate. Some moral realists would endorse this while others would insist that it need only motivate certain kinds of agents who aren’t too screwed up in some way. But, I tend to agree with your conclusion just suggest it be qualified by saying we presuming the standard sense of moral realism here.
One has to be really careful with what you mean by ‘science’ here. One way people have snuck around the is-ought gap before is using terms like cruel which are kinda ‘is’ facts that back in an ought (to be cruel requires that you immorally inflict suffering etc..).
It’s not that Harris is purely embedded in some kind of dialectical tradition. He was trained as an analytic philosopher and they invented the is-ought gap and are no strangers to the former mode of argumentation. IT’s more that Carrol is a physicist and doesn’t know the terminology that would let him pin Harris down in terms he would understand and keep him from squirming off the point.
However, I’m pretty sure (based on my interaction with Harris emailing him over what sounded like a similarly wrongheaded view in the philosophy of mind) that Harris would admit that he hasn’t bridged Hume’s is-ought gap as philosophers understand it but instead explain that he means to address the general public’s sense that science has no moral insight to offer.
In that sense I think he is right. Most people don’t realize how much science can inform our moral discussions...he’s just being hyperbolic to sell it.
Thanks for making point 2. Moral oughts need not motivate sociopaths, who sometimes admit (when there is no cost of doing so) that they’ve done wrong and just don’t give a damn. The “is-ought” gap is better relabeled the “thought-motivation” gap. “Ought”s are thoughts; motives are something else.