I'm...kinda' dumb when it comes to "stuff that means similar, but different things," I'm always forgetting which means which in such situations...So, I know one of the two terms means "whenever somebody inputs the first tag, the system automatically changes it to the second tag," and the other means "whenever somebody inputs the first tag, the system automatically adds the second tag, as well, if the user didn't do so on their own." But...which is which?

First one is alias and last one is implication.

alias: Pussy alias vagina, vulva, cunt, etc. We always use the same name (alias): pussy. If presented with another alias, it will be changed.

implies: If there is bondage in the image, it implies that there is also bdsm going on, and it also implies that someone is bound. Hence, we should also add those two tags. But there can also be bdsm (e.g. whipping, submission) without there being bondage. Bdsm does not imply bondage. A character can also be bound without there being bondage. (They can have their wrist bound to a ship mast, so that they don't fall off the ship in a huge storm... These cases are rare here in e621, but possible.)

Alias makes the first term magically change into the second term. Implication makes the first term magically add the second term.

To simplify,

If you tag dog on a post, said tag will be changed to domestic_dog which is an alias.

domestic_dog will automatically add canine, canid, canis, and mammal which is an implication.

Aliases change one word to another upon being searched or tagged
Implications are the inclusion of other tags which are related to said tag.

Kk. Thanks for the clarification!

Jacob said:
Kk. Thanks for the clarification!

...Huh. And, yet, when I went to suggest the implication, it gave me an error saying the implication already exists. I guess there's just a number of images that haven't been updated since the implication was added...?

Jacob said:
...Huh. And, yet, when I went to suggest the implication, it gave me an error saying the implication already exists. I guess there's just a number of images that haven't been updated since the implication was added...?

This is a site function to prevent multiple implication/alias applications. It simply means that there is already a forum requesting an implication for the same tag your wishing for, If you search your desired tag type in the forum you should find the forum in regards to the tag you want, where you can give your input and suggestion.

You can also search the tag in this engine as well and it will show pending requests in red.
https://e621.net/tag_implication