I would argue that sandwiches follow a prototype semantic representation in American English. That is, there are a handful of "ideal" sandwiches which are the f

I would argue that sandwiches follow a prototype semantic representation in American English. That is, there are a handful of "ideal" sandwiches which are the first thing you think of when it comes to a sandwich. Some items are conventionally not sandwiches. These items might have many similarities with things which are sandwiches, but because of their cultural or culinary significance, are in their own special category. A person may judge an object based on their relative sandwichness which is really a distance metric in which items closer to one of the platonic ideals of a sandwich than they are to a not-a-sandwich are considered to be a sandwich. This way of mentally representing categories of objects, while natural, makes forming precise, rule-based definitions of sandwich classification inherently difficult and inconsistent. Any algorithm for classifying a sandwich must either contain rules which are not universally applied in all situations, or which classifies (or fails to classify) foods as sandwiches which are not conventionally considered sandwiches. As a non-sandwich example of the same phenomenon, consider whether or not an item is considered to be furniture. A few items are universally considered to be furniture: beds, couches, desks, wardrobes. These items together form a semantic boundary, but that boundary is not necessarily uniform. Having legs certainly matters, but not all furniture has legs. Being not easily movable matters, but chairs are easily moved and if couches are furniture, so are chairs. Likewise, items which are not movable at all, such as shelves built into the wall may not be furniture depending on who you ask. Appliances have electronics, and appliances could be considered a special category of furniture, or simply not be considered furniture. Some people would classify lamps as furniture, but not televisions. The issue is that semantic boundaries are not symmetrical. Having features which differ from our platonic ideals and our prototypical example of the category are not weighted equally. Some features matter more, and all of those features together form a gestalt of sandwichness. An attempt to form hard and fast rules about which features are necessary to be a sandwich are well-meaning, but ultimately incorrect as they fail to appreciate the psychology of the sandwich, what it means to hold the concept of a sandwich in your head.