When philosophers talk about perception, they tend to focus on what we see and hear, and rarely on what we smell. But olfaction is a strange sense that deserves greater philosophical scrutiny. For example, when you see something, it's usually clear what you're looking at: a person or a chair, say. But when you smell something, what exactly is it that you're smelling?

The naive view of olfaction might suggest that when you're smelling, say, a delicious loaf of bread, you're just directly smelling a delicious loaf of bread. But the problem with this view is that often what we smell is no longer present, like when you walk into a kitchen where somebody was baking bread earlier, but now the bread's all gone. You're still smelling something—but what?

It's kind of a fun puzzle, but is it in fact that different from the other senses? Suppose, for instance, you're lying in a lovely grassy meadow at night, looking at the stars. But a lot of what you're looking at is long gone. Just as you're smelling the lingering aroma of bread, you're also seeing the lingering traces of stars.

Then again, we don't typically look at things that are so far away that the light doesn't reach our eyes till the object is already gone. That is the exception in vision—most of the time what we see is right in front of us. And that is different from olfaction. When you notice the scent of flowers on the breeze or some horrible odor emanating from the subway, what you're smelling is just puffs of air. 

Another way in which olfaction is different from senses like hearing or vision is that it's much harder to discriminate different parts of what we smell. When we look at a picture, for example, we can distinguish different shapes and colors and we can describe their relation to one another. When we listen to a song, we can hear individual chords, identify different instruments, and understand the lyrics.

What we're perceiving in these cases is quite complicated, and we have many words to describe in detail what we're perceiving. But how would you describe something like Chanel No.5 in a way that would help you pick it out of a lineup? We just don't have the words for it, because most languages are totally biased against smell. We have a zillion and one words for a pretty face, but maybe two for a nice fragrance.

Of course there may be a reason for that: we don't need those words for smells because our noses just aren't that sophisticated. Maybe we pick up on a tiny fraction of what's going on scent-wise, and it's not that important to our decision-making. After all, when's the last time you chose a book because of the way it smelled?

But some decisions clearly are influenced by smell, e.g. choosing a partner. Many scientists would say there's a lot going on there in the realm of smell. And whatever we're picking up on, we're picking up on unconsciously, which could explain we don't have the words for it. 

Of course some authors had no problem writing about smells. Marcel Proust, for example, wrote that "even when the objects of our past are long gone, smell and taste still remain for a long time like souls. And on their own most improbable droplet, they can hold up the immense edifice of memory." That's gorgeous—but it does it really tell us anything about the cookie he's writing about, much less how it smells?

Moreover, we shouldn't have to write a 3,000 page novel every time we want to describe a pleasing aroma! Maybe we could follow the wine buffs and engage in some carefully-chosen metaphors. For instance, they'll say a burgundy is serious and broad-shouldered, or a rosé is light-hearted and cheeky. But even there it's all just poetic interpretation; there are no facts of the matter. After all, what would one say to the person who claims that the rosé is actually broad-shouldered?

Well if there are any facts about smell—and maybe even some philosophically interesting truths—you can be sure our guest, Oxford psychologist and olfaction expert Asifa Majid, will help us figure out exactly what they are.