Short Version for those of you with short attention spans:
How would you write a character who is actually an hallucination of another character?

Note: I've decided to put a short version in each discussion post because I've noticed that almost no-one actually bothers to read the real version. If you do, I thank you.

Proper Version for those of you who give a damn:
One, or possibly three, of the major plot points in my story are a set of hallucinations experienced by the principal antagonist- three characters that help him to rationalise his inevitably destructive actions. These three were created by him but gradually take on lives of their own.

The Combatant, who is in control of plans, schemes, reactions and long-term goals, takes the form of a vast, powerful, dominant and almost completely undefined shape. As he becomes more 'real', he becomes an armoured but still undefined shape.

The Concubine, who is in control of fears, hopes, emotions and true feelings, takes the form of a pair of unseen hands; compassionate, kind, loving and supportive, but completely invisible hands. Her improving reality grants her a visible form- a shapely silhouette.

The Spymaster, who is in control of truth, knowledge, memory and his mind-reading powers, takes the form of a pair of blazing eyes, glowing in areas of dominant shadow; eyes that know more than they let on. His realisation allows him to move, in a patch of shadow, beyond natural shade.

My question to you all, then, is how should I write them? At the moment, I have a concept where I write them as if they were always there- as though they simply are noticed for the first time when they appear. I was wondering if I could throw it out to the group. How would you write an hallucination- based character?

It depends on the character. A question; do these three hallucinations have minds of their own? If so, are these the only parts of his mind, seeing as they seem to control all of it? Do they make the decisions, or does he talk to them? Is there a Confidence and Paranoia type thing going on (as in that episode of Red Dwarf), or do they fight among themselves? Does he call them by those titles (if he talks to them), or are they just looked at when he's talking? Do they all appear one at a time, or are they all there together? If they only appear one at a time, (which I doubt given your description) why is that?

Write them from the point of view of the character who hallucinates them. What he or she sees or reacts to, write it as if the character is really there.

The real fun comes if other physical characters are on hand to see your character either interacting with the hallucination, or trying to ignore it, knowing that the hallucination is invisible to others.

Do you mean they are a part of the character? As in multiple personalities, sort of thing? If so, you an quite happily write from the perspective of the other personalities, as they are characters in their own right.

If they are simply constructs of the main character's mind, then I'd agree with Cogito, it should be written from the perspective of the main character, or outside characters.

Sorry if I've missed the point with this...

*blinks* Well, you have successfully broken me from my three-week writing blockade. *hands out cookies*. Thank you--reading over this thread might have planted the seeds of a good idea.

On to business... you say you have the notion that they've always been there. So, perhaps the hallucinations act like they've always been there, and the main character notices them for the first time, so you'd have to write his impressions of them. If you're writing third person, you could switch and follow them sometimes, showing their points of view.

I think Cogito's notion of having others observe him would be funny and dramatic, and in fact I might steal the idea... :p.

Also, a whole lot of how you write them depends on how you want to treat them. Do you want them to be sentient, with their own personalities, or do you want them to be manifestations of the main character? What is it exactly that you want them to accomplish? That'll affect the whole outcome tremendously.

Not unheard of. The movie "A Beautiful Mind" a couple of fairly major characters turn out to be hallucinations. They are handled as regular characters with no tip-off at all. And once unmasked as projections still show up for curtain calls.

Another film with an imaginary character that is actually the MAIN character is "Drop Dead Fred"