In theory, the words "eat" and "drink" are fundamentally the same action to me: putting something (...edible?) in your mouth. Oftentimes when speaking English, I confuse the words "eat" and "drink" for no reason (even though it's my native language). For example, I might say, "I ate some water," which I hastily correct to "I drank some water." Ultimately, to me, eating and drinking are more or less the same action, which is the explanation for why I confuse these two words, although people understand me just as well if I say "I ate water." In other languages I've studied, there has always been a distinction between eating and drinking, even in other language families (eg. Korean "마시다" and "먹다" or Chinese "喝" and "吃"). Why is there this consistent distinction between eating and drinking in the languages that I know? Are there languages where there is no such distinction?
The claim that there are always separate lexemes for "eat" and "drink" is not a linguistic universal.
From Anna Wierzbicka's chapter "All people eat and drink. Does this mean that 'eat' and 'drink' are universal human concepts?" in The Linguistics of Eating and Drinking (2009), edited by John Newman:
Eating and drinking are, one might say, human universals. Or so it may seem to speakers of English, and other European languages. But what would a Kalam, or a Warlpiri linguist say about it, given that Kalam and Warlpiri have no word meaning ‘eat’ and no word meaning ‘drink’?
Of course, perhaps this merely implies that there is a distinction between languages with "ingest"-type verbs and those without. But even those with such verbs, a distinction between "eat" and "drink" is not universal. Across many parts of the Sinitic branch of Sino-Tibetan, "eat" and "drink" are not distinguished:
- Many of the Min topolects use the colloquial layer form of 食 for eating, drinking, and also smoking (of various forms). In Min Dong (which includes Fuzhounese), although 啜/歠/chuók, which is a descendant of Classical Chinese "suck", does exist for drinking liquids, it has become associated mostly with imbibing alcohol. The Classical Chinese 飲 is not present in the colloquial layer of Min.
- Shanghainese, part of the Wu family, also exhibits the single "ingest" verb paradigm. One article comparing it with Modern Standard Mandarin and with English describes how even between languages that have the eat-drink semantic distinction, the languages differ greatly in the details (e.g. breast milk, medicine / medical pills).
Adding on to the other answer, probably the most widely-spoken language without an "eat" ~ "drink" distinction is Bengali, which has adapted the native Indo-Aryan "eat" verb (kʰā-) for "drink" (historically Sanskrit pibati, cf. Hindi pī-) as well.
A funny outcome of this is that "smoking a cigarette", which uses the "drink" verb in other Indo-Aryan languages, is literally "eat a cigarette" in Bengali :)
Thai technically has different words for eating (กิน) and drinking (ดื่ม), but I've heard native speakers frequently say stuff like กินน้ำ ("eat water") when they ought to say ดื่มน้ำ ("drink water"). It's "technically" incorrect, and recognized as such by educated speakers, but it is common enough to be featured in advertisements. Google trends suggests that the former is becoming more popular over the past decade.
Where it gets interesting is that the word for "hungry" is หิว, while a common word for "thirsty" is หิวน้ำ, literally "hungry for water." Perhaps the use of หิว in both หิวอาหาร ("hungry for food") and หิวน้ำ ("thirsty") lead to an informal use of กิน. There's of course a danger in looking at only a decade in Google trends, but if the trend holds then กินน้ำ might overtake ดื่มน้ำ. This could potentially provide a trajectory that other languages followed or could follow.
We have less specific and more specific verbs so that we have a choice of which information to present.
First, consider the intransitive forms. These descriptions each paint a different scene:
- My friends are drinking.
- My friends are eating.
- My friends are sipping.
- My friends are dining.
So I suspect your question was more about the transitive forms of these verbs. But again, we have a wide selection of verbs for which specific parts of the action we'd like to focus on.
For examples in English that are fairly specific:
- I'll eat an apple.
- I'll drink some water.
- I'll walk to the living room.
- I'll drive to Honduras.
These examples can all be replaced by less specific verbs:
- I'll consume an apple.
- I'll ingest an apple.
- I'll consume some water.
- I'll ingest some water.
- I'll go to the living room.
- I'll go to Honduras.
We can also be more specific, adding more information to the verb (with some colloquialisms):
- I'll sip some water. (drink it slowly)
- I'll chug/scull some water. (drink it rapidly)
- I'll choke down some water. (drink it, but maybe it tastes bad)
- I'll inhale some water. (probably intentionally incorrect usage to imply drinking the water as quickly as possible)
- I'll swallow some water. (the speaker might be drinking or they might be saying that they're a poor swimmer?)
I'll give you an explanation based more on anthropology and logic than linguistics.
Languages have evolved from prehistory to convey verbal information that was essential for survival. Consider that Homo Sapiens have been on this planet for at least 300,000 years, hence spoken language (assuming it was a prerogative of Sapiens) predates written language by at least that much, since the first fragments of writing date back to just about 5,000 years ago.
Therefore, it can be presumed that words conveying the meaning of such basic activities such as drinking and eating should originate from those ancient times, and it is logical that there should be different terms for "drinking" and "eating", since ingesting liquids is quite a different "operation" than ingesting solids.
First of all, before humans invented drinks, the only widely available liquid was water, which was essential for surviving, even more so than food. An active member of a prehistoric community could probably survive weeks with no food, but only days with no water. So, "to drink" would probably have been almost a synonym with "ingesting water".
Drinking is an operation that can be performed quickly, while eating could require more effort. This could be important in survival: you could quickly gulp down some water before running from a predator, but chewing something while running is another thing. Not to mention that you could throw your solid food at the predator, hoping it would interest it more than your soft human flesh.
Finding, carrying and preserving water and solids require different skills and tools. Moreover, places where you could find abundant drinkable water are often particular places (lakes, rivers), whereas food can be collected in wider areas.
The very act of drinking is quite different from eating: you don't use your teeth for drinking and you can "suck" water from containers (be they manufactured or natural, e.g. a small pool of accumulated water on a rock).
Moreover, the two acts satisfy two very different needs, as far as sensations go: thirst and hunger are very different sensations, even for today's humans. It's logical that to prehistoric humans it was important to convey the difference between:
You feel thirsty --> you have to drink "something" (water, most often).
You feel hungry --> you have to eat something.
So, there are so many differences between the two actions and in the contexts where they could take place that the fact that both solids and liquids end up in the stomach could well be regarded as irrelevant, especially at the time.
All this IMO well warranted different terms. On the contrary, I would find somewhat more surprising that nowadays some languages have a term like "ingest", that means introducing something in your stomach, regardless of its liquid or solid form.
If one starts nitpicking, there are probably fewer differences between walking and running: the only main difference being speed.
In Bengali one often says "Would you like to drink some water?" as "Jhol Khabo?" here "Jhol" means water and "Khabo" is a variation of the verb "Kha" which literally means eat.
I wouldn't be surprised if this is not common but I think there must be other languages where this is the case, and the development of such seems organic enough by your own logic "categorizing consumption by mouth the same way".
Tangentially related: in Hindi one often says "Cigarette Peethahe" where cigarette is the usual english word and "peethahe" is a conjugation of "pee" which means "drink". So here we are saying "he/she smokes cigarettes" as "he/she drinks cigarettes" if translated literally. So thats another example of covering multiple modalities of consumption under the same word.
More fluff: so I would venture to guess exploring south east asian languages might net you a lot more examples here.
I do not know much about linguistics and potential differences between the words drinking and eating in languages. But as a food scientist I would say that 'drinking' and 'eating' are clearly different ways of 'consumption'. So that is the reason why, I guess, many languages may have evolved to use different words for ingesting liquid foods versus (semi-)solid foods (and sure, there might be some languages that do not have this distinction, but those do not answer the question why most languages do have the distinction). In a similar way there's a distinction between running and walking, there are all sorts of distinctions. That is one of the points of language, to classify and make distinctions.
A confusing part in the English language might be that 'eating' is also related to the general term 'consumption'. I like this confusion; When I drink a beer, then I like to consider it as eating bread.
As with everything in language, there are few universals, and things are typically conventional. However, I would like to point out that there might be a physiological basis for a distinction between eating and drinking, in that being hungry (hormonally induced) and being thirsty (detection of changes in blood composition) are two distinct biological processes which also feel very different.