Most of the time it’s not what you say but how you say it. A few complimentary words, with the right tone of voice, can become a sarcastic insult. Of the eight elements of dialogue the subtext is probably the most important yet can be the hardest to pin down.
Subtext is the meaning behind the words, the emotions within the speech. As the prefix suggests the subtext is hidden below the text. Think of an iceberg with the tip being the visible tip, with the deeper meaning underneath, out of view. Just like in real life a character should rarely say what they really mean, instead it should be subtly hidden amongst the text and in the actions of the character. If you watch any “behind the scenes” documentary about a movie and see an actor or actress asking the director about their character motivation they are referring to the subtext within the dialogue.
In the Woody Allen film Annie Hall there is a scene where Annie and Alvy are talking to each other on a balcony. While they chat the subtext of the conversation is displayed in subtitles.
When you have a grasp of subtext it helps immensely in writing dialogue. You will find that your characters will speak with a more human voice, and in a way that is more conducive to effective dialogue. That is to say it will have more snap and less directness. How often do you hear someone directly say “I’m angry”? You’re much likely to hear their exasperation through phrases such as “What the hell?” or “I can’t believe what I’m hearing!”. This is perhaps the best example of the underlying subtext behind conversation in film.
As you write any dialogue you should remember to consider the character’s attitude, their perspective on the situation, their thoughts and feelings and what they are looking to achieve in the particular scene as well the story in general.
Subtext also has another meaning. In every screenplay the main character has some sort of outside goal (the story text) as well as an inner need (the story subtext). For a character whose goal is to be able to purchase a Ferrari Testarossa they probably have an inner need to be seen as important and successful. Therefore the text of story should send the character on a path in which achieves a certain level of importance and success. This way he has triumphed even if he fails to achieve his outside goal. Without achieving his goal he may feel like a loser in the short term but the disappointment will soon lift when he realises his enhanced status. Often this realisation doesn’t even occur within the script but the audience is left with a feeling of how the character’s life will change for the better.
Practise makes perfect.
(Write as much as you can, as often as you can.)