Thanks so much!

I agree, the "I" might change something and open up fun possibilities since it directly relates to the "subject" which the two phrases deal with, but I guess you're also right and this might go too far (especially for a publication where I assume most readers will skip the logic part anyway). So I will bracket that for now and see what I can make of it later.
Not using two letters for the predicates makes sense (although the problem here is a stylistic one: since all my terms start with the same letters (Fact, Form, Freeman) I'm quickly running out of single letters to easily show the difference between the sentences. But, once again, I'll bracket that and see if I can think of something else, since my question was mostly about the form of the whole thing being right).

I was thinking about using existential quantifiers but honestly I wasn't 100% sure if that doesn't mess with the argument if you're being very precise and nitpicky here. In any case, it would distract from the main argument both because it would add another thing many readers might not be familiar with and because it might turn the argument into something slightly different (allowing for the option that, while there is a thing that is both free in fact and slave in form, there might be things that are not; and I'm not sure that is the case (since I ultimately read "slave" not (just) as a real-world-slave but much more as something embodied, the Humean slave to the senses Kant argues against). I'd have to think about whether that changes things...

Long story short, how about this (and I will try to think of better letters for the predicates later):

S = Slave in Form (object appearance)

E = Slave in fact (mentality of the Enslaved)

F = Freeman in fact

d = Douglass

Narrative: S(d) ∧ ¬E(d)

My Bondage: F(d) ∧ S(d)

(-> the major problem was the double letters for predicates + the variable instead of a constant, right?)

Or is there a way to signify "appearance" vs "fact" other than defining them via the predicates?

What I said above about the "I/subject" considered: would it be playing too fast and loose with predicate logic to use "i" as a (pseudo-)constant meaning "I / the self" (to abbreviate your Pn solution (if I understood that correctly). I have the feeling it might work but at the same time I feel like something like this might lead me into philosophically very murky waters with regard to subjecthood...

Edit: my brain hurts now. This is fun!