Wait, Is Cereal Actually Soup?
Semantic debates about whether certain foods do or do not slot into particular categories are like Rorschach tests. Whether a glass is half empty or half full, a rare beverage contender, is among the oldest and most obviously philosophical of popular culinary quibbles. "Is a hot dog a sandwich?" is the most famous; the "what time is the Super Bowl" of edible arguments.
Then, there are more niche or even regional proffers, often also sandwich-related. Is a lobster roll a sandwich? Is there a difference between one from Maine or Connecticut? What about a gyro, or any of the open-faced melts in creation? Some proposals deliriously veer into the absurd: Isn't wine juice? Aren't we drinking juice right now?
Whether cereal is soup falls somewhere in between, requiring more in-depth consideration. And your answer (since there isn't necessarily an absolutely correct one), as with all of these mostly harmless little imbroglios, provides the quickest glimpse into your very soul. (And, for the record, a hot dog is not a sandwich any more than a lobster roll or gyro are, but open-faced melts win the designation; and yes, we are drinking juice right now.)
In favor: Cereal is soup
Anyone who tries to tell you that cereal is not soup is so willfully incorrect that they must be trolling. Cereal's standard presentation and consumption so closely mirror soup's own presentation and consumption that they are not only sisters, but fraternal twins. Barring any outliers like Cinnamon Toast Crunch on ice cream for dessert or a shot of gazpacho on a passed tray at a wedding, both soup and cereal are served in bowls and eaten with spoons. If it looks like a duck, swims like a duck, and quacks like a duck, that's a duck soup, baby. Or cereal.
Delve deeper than appearances and your soup and cereal's compositions are also equivalent. Excluding, again, something like a consommé, you have a liquid base somewhat suspending the main solid ingredients that typically identify the dish. The chicken and noodles to your broth, for example; the Corn Pops to your milk or dairy substitute. And given all the wonderful cold soups known to humanity (borscht, vichyssoise, and cucumber, to name a few), cereal's temperature is impervious to refutation, so don't even try it. All of this makes soup the broader genre. Soup isn't cereal. But cereal is soup.
Opposed: Cereal is not soup
Most of these food-defining questions, including this one, can be answered by conventional wisdom. If you invited people over for sandwiches and you served them hot dogs, lobster rolls, or gyros, nobody would be mad, but it would probably be a conversation starter. Maybe when you were out of the room. Likewise, if you ordered a "steak" in a restaurant, somehow absent any other context, and you were served the tuna variety, you would almost certainly send it back. Outside of some Clooney-esque film-set prank, the same concepts apply to soup and cereal.
Admirable as the whimsically abstract, perhaps chemically altered thinking that might lead an otherwise reasonable person down the cereal-is-soup path, we live in a concrete world. One could wade through thousands of soup recipes online without ever finding cereal in their search; you needn't cook cereal, after all. Even humorously conflating the two at the diner would lead to little more than eye rolls from the staff. And you might not be forgiven if you delivered a great big pot of sweet cereal to a sick friend in lieu of the expected savory chicken noodle soup. Fortunately, however, soup and cereal are vast and varied enough to have their own endless iterations without ever having to meet. So, arguably, cereal is not soup. But it doesn't need to be.