Requested feature overview description.
...bla.

I propose a feature where every tag on a post can be marked as "weak". Such tags are used as a way to determine when tags are there based on assumption, rather than being purely visible. In cases where there's limited possibilities, the "weak" tags would determine all the possibilities. I'm not sure which notation would be the best way to mark tags as weak. tag% tag^ tag? *tag (tag) {tag} [tag]. Well, let's use a question mark for now, so "male?" tag on a post would mean the tag male is weak.

Examples:
1. You have a post where a character has breasts and penis, but you can't see if it also has pussy or not.
Currently tagged as : dickgirl.
Using weak tags: dickgirl? + herm?
Explanation: The two tags cover all the options, rather than say that there's no pussy because we can't see it.

2. A floating penis.
Currently tagged as: male + disembodied_penis
Using weak tags: male? + disembodied_penis
Explanation: We're assuming the male character exists even though we can't see it. This is currently realized as sort of an exception to TWYS. But using a weak tag, it would not be an exception but common logic.

3. A female character with a cloaca.
Currently tagged as: cloaca
Using weak tags: cloaca? + pussy? + anus?
Explanation: The cloaca is inherintly weak tag, because you already need to assume that there's an anus inside it, for it to be a cloaca at all. But if you assume that it's a cloaca, then you also need to assume that is serves as an anus. And as a pussy.

4. A character with an ambiguous gender.
Currently tagged as: ambiguous_gender
Using weak tags: male? + female?
Explanation: We don't know which one it is, but it's gotta be one of the two.

Well, besides adding an option to mark tags as weak, we would also need to add an option to search for weak tags, and not just strong ones. This way, searchers would be able to more clearly define whether they want to search only for definitely visible things, or also things that can be assumed.

Why would it be useful?
It would make tagging more powerful. It would make searching more powerful. It would allow for removal of all ambiguous_* tags. It would begin a whole new era of assumption-based tagging. Huehuehue.

What part(s) of the site page(s) are affected?
Database structure. Search engine. Tag parsing.

...

Well, it's just an idea. Probably a very bad one. You may flame me now.

No to all of them. Weak tags would not serve a purpose for finding what you want. This would literally prevent people from finding what the tag is meant to represent, searchable or otherwise.

The way I see it, weak tags would allow people to tag things which would normally not be possible, and other people to find by specifying that they want to include posts that contain weak version of a certain tag.

So please elaborate on what you mean, perhaps by including an example?

Delian said:
The way I see it, weak tags would allow people to tag things which would normally not be possible, and other people to find by specifying that they want to include posts that contain weak version of a certain tag.

So please elaborate on what you mean, perhaps by including an example?

The same reason disambiguation pages need heavy work on (as of when I worked on them) this is basically a lazy project. If you don't know the tag, leave it to another person. TWYS is fairly set in stone for most of your examples, cloaca is the only one I do not have experience with.

Tags need to work for blacklisting as well, leaving open-ended tags that may be argued, like dickgirl when confused with herm or female, as dickgirl? Would not benefit said blacklists. This is where experienced taggers and admins come in, and this is where the flaw of disambiguation pages come in as well. As stated, either do it if you know how to or let someone else do it, because guessing or speculating doesn't benefit everyone (mind you, nothing ever will, but minimizing it is better than leaving them all alone).

-1. This would mean tagging every ambiguous_gender post with male? female? intersex? for one thing. Every nude picture from the waist up would have to be tagged topless?. Every male character would be herm? unless we could see them from below. Every character with their eyes_closed would have red_eyes? yellow_eyes? blue_eyes? heterochromia?.

Don't tag what you can't see. This is why we have the TWYS policy.

I think you raise some really good points about current tagging issues, but I cannot disagree enough with the proposed solution. Weak tags would mean anyone could tag anything as whatever they want because fuck it, it's a weak tag so it shouldn't matter, right? And it would indeed make searching a mess, unless some advanced search option with a [Include weak tags] checkbox were included, but it'd require a total overhaul of the search engine for virtually no point. (I think? I don't actually know how hard that'd be.)

The things you're trying to solve with this idea are issues that come up a lot, but I'm afraid this wouldn't solve them.