I've been too busy to post for a while, which is upsetting, so I decided to come up with something quick.
I'm compiling a laundry list of commonly taught notions in linguistics which are probably best left in the past. Most of these are found in almost any linguistics textbook. I'm asking for help, brainstorming things that should be purged from the collective consciousness of modern linguistics.
1. Phonemes and allophones. My phonologist colleague Chris Golston pointed out that this is a distinctly Structuralist construct that is in all the textbooks. But it is not a part of current phonological theory, by most accounts. The old notion of phonemes, separate from morphological alternations, is tied to the "systematic phonemic level" of representation, which hasn't been used for decades. Instead of explicitly talking about allophones like they were items, we could just talk about nondistinctive variations of sound.
2. Morphological typology. Can we please stop talking about Humboldt's scheme of "agglutinating", "isolating", "synthetic" and "polysynthetic"? This is a pointless classification.
3. Function vs. content words. My colleagues still believe in this one, but I think it is pretty hopeless. Somebody told me that a content word is one whose meaning is a "cognitive concept," while a function word is one whose meaning is definable as a usage. Is there some accepted definition of a cognitive concept apart from a linguistic usage? I don't think so. Just a lot of debate and competing claims getting nowhere, I thought.
4. Inflectional vs. derivational morphology. I think this is likely a false dichotomy.
That's what I could come up with today. Let's add some more later.