Most like to divide Synesthestic experiences between Projective and Associative.
Projective Synesthesia is said to be experienced externally, as real as your other senses. For example physically feeling your arm being pinched when listening to violin music.
Associative Synesthesia is said to be experienced in the mind. For example, associating the colour red with the word poetry. For those with aphantasia this can be in the form of associating the concept of the colour red to the word poetry. You needn’t be able to experience senses within the mind.
I’ve tried bringing this up in the mainstream Synesthesia community before, but get mostly ignored. These two options simply don’t cover all varieties of Synesthetic experiences.
Another, lesser known attempt at division has been made in the form of Localized and Non-Localized Synesthesia.
Localized Synesthesia is when your Synesthetic experience is focused within a specific area. For example, sensing January to be located 3 inches and 30 degrees left from the tip of your nose.
Non-Localized Synesthesia is when your Synesthetic experience is not focused within a specific area. For example experiencing the number 4 to be female. The female-ness of 4 in this case, is just a fact, an attribute, not a location.
Again, surely this cannot cover all varieties of Synesthesia, at least in a meaningful way.
When I look at my own Synesthetic experiences, I struggle to place them on these dichotomies. I basically have 2 variations of Synesthesia, ones that manifest in Mindscape and ones that manifest in my Synesthesia Layer.
Mindscape is what I call my inner universe, where I fantasize and experience my plurality. The Synesthesia that happens here is my OLP. Ordical Linguistic Personification. For me letters, numbers, zodiacs, the seven sins, and some other random things exist as people in Mindscape.
Synesthesia Layer is a layer separate from both reality and the mind. It is 3D in nature. The Synesthesias that happen here are my Grapheme-Colour and my Auditory-Spatial. For example, when I am reading text I can fully see the actual letters, which are often black. I’m not imagining their colours, they’re right there, but they’re not. I can’t actually see them, but I can inside of the Synesthesia layer. It activates automatically whenever there is text. Some colours are more in the foreground and others in the background, some colours are more dominant and others faded. E’s can vary between mint and aegean blue. Mint e’s are often one of the most faded and backgrounded colours. P’s are always red, dominant and foregrounded. Then, when I’m listening to music I can feel the music move through and around me inside of the Synesthesia Layer. It can be textured and coloured. I call the individual moving parts vectors. This has been the hardest Synesthesia to actually describe to others.
Now, is Mindscape Associative because it’s in my head, or is it Projective, because Mindscape is my private alternate reality? Is Mindscape Non-Localized because as I said before, ascribing genders and other attributes to things aren’t locations, or is it Localized because those people actually exist somewhere in Mindscape? Is my Synesthesia Layer Projective because it doesn’t occur in the mind, or is it Associative because it doesn’t occur in reality? Am I being too autistic about this? Possibly.
Optional Bonus Objective: Guess which one of the 4 examples I gave is actually close to one of my own experiences!