The films Life as We Know It and In the Land of Women illustrate 'character as prop' only too clearly. In the first instance, the prop is the baby whom two singles must raise after the infant's parents are killed in an accident. In the second, the prop is the elderly grandmother whom the protagonist--her grandson, a writer of soft-core porn movies--volunteers to baby-sit, so to speak. In each instance, once the prop serves its purpose, it is relegated to the background of the plot, and fails to drive the action.
|Olympia Dukakis a prop for Adam Brody in In the Land of Women|
What do I mean by 'driving' here ? Glad you asked. I mean that this character's needs wants or actions impose continuing or escalating demands which in turn increase the stress or conflict within the protagonist(s). Which stress/conflict can only be relieved/resolved at some real cost to themselves and induce change. That's what creates the dramatic energy in the situation as it advances (or degrades).
In In the Land of Woman, the protagonist never faces any demands from the 'prop' character, and pays no price whatsoever for his involvement with her. At least in Life as We Know It, the protagonists do eventually pay a price for assuming parental responsibillities.
There are numerous examples where the scenarist has taken care not to reduce 'inciting characters' to pieces of furniture : Uncle Buck and Three Men and a Baby come to mind, and these characters create palpable stress or conflict for the protagonists.
[ (6/2/2011 Update : The film While You Were Sleeping represents an excellent example of how skilfully to employ a 'prop-character'--a sort of male 'Sleeping Beauty' if you will--without completely reducing said character to cinematic furniture. ]
In some cases, the 'prop-character' has no role in the original inciting incident, but is introduced later in the scenario, and personifies a conflict that is latent within the scenario : e.g., in Woman of the Year, the Greek war-orphan whom the title character adopts but treats like a prop, both personifies and exposes the shallowness of her marriage.
So, note to self : no prop character, unless it's a muta persona, like say, the corpse in Porky's.