A friend of mine recently returned from Ecuador having tried (and enjoyed) the local speciality ‘cuy’ – that's whole, spit-roasted guinea pig. Just a month before, the same friend had paid several hundred pounds for a vet to remove a tumour from his pet gerbil. This is the sort of ‘double-think’ that Legge points to in her poem, an example of a more general inconsistency permeating our attitudes and behaviours towards animals.

This accusation of inconsistency has bite, even against those meat-eaters who draw a clear moral distinction between humans and other animals. Most of these people believe it's wrong for a dog to be left on its own all day, because it will be ‘bored and lonely’. Yet many of these same people are unmoved by the knowledge that pigs are kept in single stalls for much longer periods. Evidence suggests that pigs have similar needs for intellectual and emotional stimulation to dogs – which is why providing toys has been so successful in reducing ‘losses’ in pig farming.

Now, it might be that there are ways of resolving this inconsistency. The special value of this metal loop on my finger comes from the way I relate to it – as a symbol of love for my spouse – rather than as a result of any intrinsic properties. In the same way, perhaps we can say that the special value of our pets results from the relationships we have formed with them. But even if this particular inconsistency were resolved, there are endless other inconsistencies remaining in our attitudes and practices towards food. We might focus on ‘buying local’ and reducing air miles whilst in the vegetable aisle, but forget this by the time we get to the cereals. We might take care to purchase free-range eggs, but not worry about this as we squirt out the cheapest-brand mayonnaise.

As someone who doesn't eat meat, I'm used to accusations of inconsistency being thrown my way. I'll check with the waiter whether a particular dish is vegetarian, and my fellow diners will point to some other aspect of my behaviour – driving an SUV, the leather strap on my bag, and even, on one occasion, riding horses – that they perceive to reveal the inconsistency in my ways.

I find this reaction odd. I tend not to evangelize about vegetarianism, and so somehow it is just the mere fact that I believe there to be something morally questionable about meat-eating that gets their goat. Perhaps there is an expectation that, because I am taking a ‘moral stand’, I should have higher standards of consistency. But what's particularly odd is that these accusations fly before finding out what motivates my behaviour. And if you believe that animals should not be made to suffer for the momentary pleasure of humans, it isn't necessarily inconsistent to engage in this combination of activities.

In fact, depending on what your moral motivations are, applying them consistently can result in some fairly unorthodox diets, which don't fit into our neat categories of ‘vegan’, ‘pescatarian’ and so on.

You might, like one philosopher-friend of mine, believe it's wrong to eat animals that surpass a certain threshold of intelligence, and consequently exclude pigs and octopuses from your diet. There's plenty of evidence that these are among the most intelligent of the organisms that we commonly see on menus. Six-week-old piglets learn to navigate their way to food using a mirror within a few hours, something that takes human toddlers significantly longer. Octopuses, the large-brained Einsteins of the invertebrate world, can make use of tools to obtain food. They have even been known to open child-proof jars, something which I am yet to master.

Alternatively, you might think it is wrong intentionally to cut short the life of a healthy animal. In which case, you might be happy eating a lamb who broke its neck whilst gambolling, or picking up some road-kill for dinner.

You might be concerned about the environmental impact of livestock farming and over-fishing, in which case, you should aim to reduce, but not necessarily eliminate, meat and fish from your diet. One kebab after a night out isn't a sign of weakness – it's allowed within this diet. That might be one reason why ‘reducetarianism’ is gaining popularity.

Or, like me, you might be worried by the amount of suffering that an organism endures before reaching our plates. Since we can't access the subjective experiences of other humans, let alone other organisms, we can never know the extent of animal pain and how much it resembles our own. But from looking at their behaviour, alongside studies of their brains and nervous systems, we can speculate that some organisms have less capacity for suffering than others. It was this reasoning that recently led me to try snails (an experience I will not repeat in a hurry). Although snails display avoidance behaviour such as moving their ‘tails’ off a hot plate, they don't have a spinal cord or a single brain, and many scientists think it unlikely that they experience anything analogous to the pain that we do.

Given the variety of moral justifications available to defend one's diet, accusations of inconsistency ought to be made with caution.

We would also do well to remember that consistency is not all we should care about in our attempts to live as good human beings. We can imagine a Nazi officer who was highly consistent in the way he lived his life. He always told the truth. He respected his fellows as equals. He provided for his family. And he methodically and efficiently killed Jews. Clearly we cannot evaluate this man's life as morally good. The point is that we care not just about applying our beliefs consistently, but also about having the right moral beliefs.

Moreover, we might think that some kinds of inconsistency are worse than others. The inconsistencies with eating discussed so far are all at the level of praxis – they are failures to apply our morals in a consistent way. But there is another kind of inconsistency which seems more deeply immoral, and more aptly called hypocritical. This is where there is complete incongruity between our moral beliefs and our behaviour, and where no steps are taken to rectify this mismatch.

Many of us are quietly aware that we don't have good reasons for the sharp distinction between human and non-human animals required to justify our culinary practices. As the Judaeo-Christian foundations for Western morality have crumbled, humans can no longer be viewed as the pinnacle of God's creation, distinct from other animals because endowed with ‘the breath of life’. Moreover, evolutionary theory suggests that the differences between us and other animals are differences in quantity rather than kind. These thoughts may prompt us to consider extending our moral circle to include animals, just as we have done in the past to other races and to slaves.

Many people, in their more reflective moments, will concede these points and other arguments against eating meat. But this acknowledgement fails to produce any action: they don't even try to put these beliefs into practice.

The philosopher Jonathan Wolff gives voice to a fairly common experience when he observes that although he finds himself ‘very sympathetic’ to the moral case for vegetarianism, he recognizes the ‘peculiarity’ that ‘I do not find such arguments, however intellectually compelling, of very strong motivational force’ (Ethics and Public Policy, 32).

This phenomenon does not support optimism over the fruitfulness of philosophy for improving our behaviour. We can recognize the force of an argument, whilst feeling no compulsion to try to live out its implications.

Instead, we erect barriers that stop us from having to acknowledge the realities of what we are doing. We shop for ‘pork’, not ‘pig’, and this comes in neat packages that no longer bear witness to its origins. We build our abattoirs out of towns, hidden, so that people don't have to think about them. (Remember Paul McCartney's comment that ‘If slaughterhouses had glass walls, everyone would go vegetarian.’) This strikes me as a different level of inconsistency from (for example) someone who always buys free-range eggs but doesn't check the label on her mayonnaise. The mayonnaise-buyer is, at least, taking some steps to eat ethically, rather than blocking out the moral issues entirely.

Living in an ethically consistent manner is hard. This is particularly so when it comes to eating, where we often face a time-pressured choice between numerous options, whilst being under-nourished in the information needed to make a good decision. But it does seem right that we should at the very least aspire to eat in a way that accords with our beliefs.

I am most certainly not a model of how to eat consistently. But I am trying.