He was fearful.
He was fearless.
It was a fearsome beast.
It was impermeable.
We have many AdjectiveOf adjectives, which just refer you to the object – heart and cardiac, vein and venous, but then we have other adjectives which refer to a relation, and may refer to the
Process
Subject
Object
or several, or any of these in a particular state.
He was fearless.
He didn’t fear anything.
It is not the same as he couldn’t fear anything, so we get
The person is capable of fear (the relation exists, so they are not a psychopath), but there is nothing that they do fear – anything will match BaseThing.
A permeable membrane.
This is so simple that a class of adjectives would do (we already have it – AbleAdjective indicating the object of a relation, so permeable is a description of something that can be permeated). Not all "-able" adjectives are like this.
But "capable" is not so easy.
He is a capable person.
"he is capable" means he is capable of doing anything a person can do – we don’t know whether he does do it.
"He is capable of murder" changes the object, but still gives us a true on the existential pin of the relation - he could do murder.
Adjectives like
Liable
Available
Reputable
Suitable
Amenable
Agreeable
Feasible
Indubitable
Reliable
are not so easy.
Some words just need a collocated form of the verb - ToRelyOn for "reliable" – able to be relied on, while others, like indubitable, operate on the existential link.
Some words have changed their meaning – "awful" – or the root has gone out of fashion or means something entirely different – "culpable", "egregious". Some adjectives have multiple meanings – "wary" may mean watchful or careful or (one meaning of) suspicious. In these cases we can’t avoid using relations and states (and MEANING operators).
"negligent" is a good example of a word that needs a structure – a person who is negligent neglects something that he is obliged to do.
How is this going to be relevant to medicine? Well, "negligent" already is. While we are still dealing with physical objects, a heart, a lung, the complexity is not so great, although pain can be a sticky area. Even a simple medical description has adjectives like "concomitant" and "judicious", which just can't point at other objects. As the description delves deeper into the mindset of the clinician and the patient, the adjectives will become more complex.
Once we stray into the specialties of psychology or psychiatry, it will be essential to build complex structures to define adjectives with complex meanings.
See Metastasis for a complex definition that applies to an adjective - metastatic.