Screenwriting: Visual, External, Present Tense
A screenplay is a blueprint for a film — its purpose is to communicate story visually and efficiently to a director, actors, and production team. Every aspect of screenplay format serves this function. The three core constraints of screenwriting that most significantly differ from prose fiction: Visual only — what appears on screen must be seeable and hearable. You cannot write a character's interiority in action lines ('She remembered how her father had smelled of sawdust and coffee') because a camera cannot film memory unless it is a flashback. Interior life must be externalized: shown through action, behavior, and dialogue. This is the screenwriter's fundamental creative constraint and creative opportunity — to externalize everything. Action-external only — a screenplay action line describes only what is visible and audible on screen in the present moment of the scene. No backstory, no explanation of motivation, no narrative commentary. 'She picks up the phone, puts it down, then picks it up again' is a correct action line. 'She hesitates, uncertain whether to call him, thinking of last October' is not — the thinking is invisible. Present tense — all action lines are written in present tense, third person ('INT. KITCHEN — NIGHT. SARAH enters, glances at the stove, then fills the kettle'). Screenplay format conventions: slug lines (INT./EXT. LOCATION — DAY/NIGHT), action lines (12-point Courier, single-spaced, between 1–4 lines each), character names (ALL CAPS, centered above dialogue), dialogue (centered, narrower margin than action lines). One page of correctly formatted screenplay equals approximately one minute of screen time — a feature film is 90–120 pages. Scene structure in screenplay: each scene has an entrance and exit, a purpose (at minimum: something changes from the scene's beginning to its end — a character knows something new, a relationship shifts, a situation escalates).