Name a vegetable. It’s easy right? Sweet potatoes and carrots are vegetables, obviously. Onions perhaps? But what about lettuce, for example?

And we have all met those who insist that a tomato is a fruit. Then there are others who argue that because it’s not sweet in the same way as an apple or a pear, a tomato is more properly categorised as a vegetable.

To get some clarity, we asked the audience of BBC Earth for some help.

“You're BBC! Why are you asking us if this is a vegetable?” wondered Kimberly A. Brooks. “Is that the best you can do? Disappointed.”

If we apply such fruit-based logic, then we would have to banish dozens of other kitchen staples from the vegetable drawer

“Ummmm,” replied Leah Kimmet. “It is a question posed to stimulate discussion because it is one of those debates that has never been conclusive.”

“This is the most interesting comment thread I’ve ever seen,” said Harry Trevva-Taylor Blake.

Precisely. Our question was particularly pertinent for Marc Trevelyaи, who was in the midst of eating a salad comprised of lettuce, carrots and apples.

As this is BBC Earth, I put the question to Wolfgang Stuppy, research leader in Comparative Plant and Fungal Biology at the UK's world-renowned Royal Botanic Gardens, Kew & Wakehurst Place.

On the little question of whether vegetables really exist, he could not have been clearer: “No, not botanically,” he says. “The term vegetable doesn’t exist in botanical terminology.” Tamara Kershner’s comment echoes this edict: “Vegetable is a general term that doesn't exist in the biological world.”

From a biological perspective then, there is no such thing as veg. There are just plants.

I throw some hypothetical vegetables at Stuppy to see how he responds. But the radishes and carrots on sale at the greengrocers are not vegetables to a plant scientist, they are merely the roots of radishes and carrots. Botanically speaking, onions and garlic are bulbs. Potatoes and Jerusalem artichokes are tubers. Asparagus are stems. Lettuces are leaves. Cauliflower and broccoli are inflorescences. Apple and pears are fruit.

So is that it? Vegetables do not really exist?

Not quite, because veggies might have a place in the kitchen. “Vegetable is a culinary term,” says Joshua Sammy. I refer to On Food and Cooking by Harold McGee, something of a holy book for foodies. “Vegetable took on its current sense just a few centuries ago and essentially means a plant material that is neither fruit nor seed,” he writes.

If you put your botanist’s hat on they are fruits. If you put your chef’s hat on they are vegetables

Yet even here, within the culinary sphere, the definition of vegetable seems to rest on the definition of a fruit. A fruit, says Stuppy, is “any structure produced by a plant that does or is meant to contain seeds.” So according to McGee, the tomato does not qualify as a vegetable (as most of you knew).

But if we apply such fruit-based logic, then we would have to banish dozens of other kitchen staples from the vegetable drawer, including cucumbers and courgettes (Pierre G. Bélance), squash and pumpkins (Brock Burch), peppers and corn (Ali Ware), beans and aubergines (Lee Chi Pan Mark) and so on. Mushrooms aren’t even plants so they can’t be vegetables either. The same for seaweed.

Andrew Schaug has a useful way of looking at the tomato: “It’s technically a fruit because it contains seeds. It’s a vegetable because it’s part of a plant and used as a savoury ‘vegetable’ in cooking,” he says. Several others – DS Deopa, Stephen Olsen, Mahendra Bishnoi, Alan Hutchinson – expressed a similarly practical position: there are some plants that are fruit but are used as vegetables. “If you put your botanist’s hat on they are fruits,” says Stuppy. “If you put your chef’s hat on they are vegetables.”

So ask a botanist to define a vegetable and they will say they cannot, as such a definition does not exist.

Ask a chef, and they might define a vegetable as plants that are neither fruits nor seeds.

Ask a lawyer, however, and they might say it depends where you live.

That’s because the existence of vegetables has been accepted in law – and all because of that age-old dilemma of whether a tomato is a fruit or not.

More than a century ago, the Supreme Court of the United States ruled on the status of the tomato in the infamous case of Nix versus Hedden.

Live outside the US, and things again become confusing

Several of you, including Lester Chasteen, Benny Thomas and Andrew Schaug, were aware that the Tariff Act of 1883 decreed that imported vegetables, but not fruit, should be subject to tax. With a financial interest in tomatoes, the Nix family argued along botanical lines, that the tomato is a fruit so they were exempt from duty. The court begged to differ, siding unanimously with federal officer Edward Hedden: the tomato is a vegetable.

But live outside the US, and things again become confusing, as this is not the judgment of lawyers in the European Union, at least in respect of European Union Council Directive 2001/113/EC. This ruling, on the content of fruit jams, jellies and marmalades, clearly states that tomatoes “are considered to be fruit,” as are rhubarb stalks, carrots and sweet potatoes.

As a result, a jar of rhubarb, carrot or sweet potato jam – none of which contain any botanical fruit - must state the percentage of fruit they contain.

Which brings us full circle. Do vegetables exist?

Botanically no.

Culinarily, yes.

Legally, maybe.

Easy, isn’t it?