There's a lot to like about Sam Harris's views on morality . In fact, I suspect that even his most vocal critics agree with him on a vast majority of what he has to say. His advocacy for a scientific engagement with morality is warmly welcomed, as is his commitment to go beyond the old God versus no-God debate to suggest a positive agenda to build a secular morality devoid of supernatural meddling.

But there's one sticking point - one to which Harris continues to apply glue - and one against which people like myself and Russell Blackford continue to rebound. That is Harris's insistence that science can describe morality all the way down.

Harris suggests that science doesn't stop at the descriptive water's edge, but extends so far as being able to establish our most fundamental values. His brand of bald naturalistic realism is not only extreme but, in my opinion, overshoots his objective. And in so doing attracts criticism that in turn detracts from the merits of his view.

Harris, being understandably tired of seeing empirical research sidelined in moral enquiry, is keen to challenge the dogma that reinforces the descriptive/normative gulf.

His main targets are Hume's is-ought gap, along with Moore's naturalistic fallacy. These are commonly interpreted as saying that science can tell us how the world is, but it cannot tell us how the world ought to be.

Science can tell us what things cause pain, but nothing it can say about particles and nervous systems can tell us that pain is bad. Science can tell us how zygotes develop into embryos and on into foetuses and then into people, but it can't tell us where to draw the line in terms of what counts as a fully-fledged moral agent worthy of a right to life.

The result has been a divorcing of empirical research from moral philosophy, particularly since the early twentieth century. Harris suggests the is-ought gap and naturalistic fallacy have gone too far in declaring that empirical research is entirely separate from moral enquiry.

And he's dead right.

But instead of accepting a modest victory, and making a modest reintroduction of science into moral philosophy, he seeks an unconditional surrender from moral philosophers, and in doing so (to push the metaphor) he suffers a Pyrrhic victory.

However, it's not Harris' emphasis of science that is the cause of so much philosophical criticism directed against his theory. It's insistence on a particularly extreme brand of realism.

In metaethics - that branch of moral philosophy that doesn't seek actually to guide moral behaviour, but to understand what terms like good and bad mean - there are two broad schools of thought.

In the blue corner, moral realists suggest that moral statements - like, say, "capital punishment is wrong" - are the kinds of things that can be true or false.

In the red corner are moral anti-realists , who argue that moral statements aren't true or false, but rather are either assertions about how we want people to behave (non-cognitivists) or just wrong entirely (error theorists).

Sam Harris aligns himself with a school of thought that is solidly in the blue corner by advocating a particularly uncompromising brand of naturalistic moral realism. This suggests that what makes moral statements true are natural facts about the world.

But this stance is deeply philosophically problematic. And posts like those of Russell Blackford outline in exhaustive detail why.

Even Harris's response to Blackford suggests that he hasn't fully grasped how extreme his view is, and that he doesn't need to push so far in order to win a place for science at the moral table.

In defence of his naturalistic realism, Harris likens morality to health:

"Clearly there are scientific truths to be known about health - and we can fail to know them, to our great detriment. This is a fact. And yet, it is possible for people to deny this fact, or to have perverse and even self-destructive ideas about how to live."

The hope is that we will all concede that health is something real, and there are real facts discoverable by science that tell us what is and what isn't conducive of health.

Health can remain a somewhat elusive concept - it's a property of living things, but is not directly observable, for example - but it's still real. And it's comfortably transparent to scientific enquiry. So too, argues Harris, is morality.

The thing is, Harris isn't the first to draw a parallel between morality and health. Another moral realist, Paul Bloomfield, has dedicated virtually his entire 2001 book, Moral Reality , to fleshing out this analogy and using it to defend moral realism.

"Moral properties have the same ontological status as healthiness or other biological properties. If being invisible to observation and not playing a role in causal explanations are not problems for realism when concerned with being alive and healthy, then these cannot be problems for being good or bad or getting it right or making a mistake. If we are committed to realism about other properties with these attributes (these properties of properties), then moral properties having these attributes cannot be a problem for realism with regarrd to them. So we arrive at a form of moral realism that takes its lead from the metaphysics of physical health."

The analogy is intriguing. But it's ultimately a dead end in terms of justifying the kind of naturalistic realism that Harris (and Bloomfield) advocate. However, the reasons why it's a dead end are illuminating.

The analogy, if it holds, doesn't actually reinforce full blown realism. If anything, it supports a kind of anti-realism.

And I believe if Harris were to embrace the moral-health analogy in this anti-realist way, his entire approach to morality would be stronger - and people like myself and Blackford would only be making noise about how good it is instead of spending the bulk of our words on our disagreements.

The thing with health - and the problem with the health-morality analogy - is that one can have exhaustive knowledge of the facts about health, and the facts about what one ought to do to be healthy, but they can still rationally (if imprudently) say "So what?"

There is nothing about the facts of health that compels one to pursue health, nor that condemn that individual as being irrational if they don't value health and go off and guzzle doughnuts. There needs to be an extra premise - that one ought to pursue health - that doesn't appear to follow from the facts about health.

Likewise, someone could have exhaustive knowledge of all the facts about well-being (assuming that's even possible) and still say "So what?" Yes, this person is probably acting imprudently and against their self-interest, but there's nothing rationally binding contained within these facts that commit them to pursuing well-being.

This is precisely what Hume was getting at with his is-ought gap. There needs to be an extra value-laden premise added into the mix with all the natural facts to give morality its practical oomph.

Certainly, the is-ought gap has been overstated by philosophers, but there's something about it worth taking seriously.

The facts about health and morality might be real. But the lynchpin of morality - the commitment to pursue health/well-being - is not established by scientific fact, only by our own agreement to pursue them.

And here's the rub: this isn't even remotely a practical problem for morality because, as a matter of empirical fact, virtually everyone is already pursuing health and well-being.

We're social animals, after all. Being animals, we pursue health. And being social, we pursue morality. And if everyone is pursuing these things, there are things they ought to do, and things they want others to do.

Morality is really a deep kind of prudence: if you value wellbeing, do X, and demand that others do X too.

And as virtually everyone values well-being, then all's good. But what about those who don't value well-being, and who by doing so threaten the wellbeing of others?

Well, they're kept in line by those who do value well-being. Hence, moralizing, norms, laws, social contracts, and so on.

And if, one day, everyone decided not to pursue health and wellbeing, we'd probably all die out. And we'd die fools (if rational fools).

So you can be an anti-realist at the bottom - suggesting that pursuit of health or well-being is not written into the laws of nature - and be a realist up from there, and you end up with a moral system that is basically identical to the one Harris is advocating.

Science doesn't have to dictate morality all the way down in order for it to play a pivotal role.

Were Harris to adopt such an anti-realist position, he'd gain much and lose very little. He'd still have a strong case for the role of science in moral enquiry, and he'd still be able to build a robust moral system that promotes the values he wants.

He'd have to argue (philosophically) about well-being, what it is and whether there are any better ways of defining the object of morality, but that's an argument into which he'd be most welcome.

Tim Dean is a science journalist and editor of Australian Life Scientist magazine. He is completing a PhD in philosophy at the University of NSW, researching the evolution of morality, and he blogs at Ockham's Beard. If you want to join in the discussion about secular morality and secular religion, you can email Tim at secular.morality@gmail.com.