Having a free input dialogue system was a challenge, although the topics within the game (like what is love, how to manage a relationship, decide between what's logic and what are your feelings, death, etc) are always a matter of discussion and there are no real answers to the questions they rise. For this reason we thought that was necessary to let the player to freely express her opinion instead of just providing fixed options.
A dialogue though should have a direction, especially if you're trying to tell a story through it, so we needed to come up with some limitations. The main ones are probably the narrative frame and the dialogue itself. You'll be a mantis, in a relationship, and you'll talk about what to do about it. All of this helps a lot in limiting the scope of the conversation. The player will act in a well defined situation, so she's expected to provide context-related answers. In order to help her in doing so the writing is fundamental. We used several techniques, but the ones that we used the most are these three:
- using conversational hooks in the lines of the partner to induce the player towards certain topics
- use questions to make the player feel engaged and stay in role
- use sentences that don't require specific answers, but that provide hints on the mood of the partner, so the player can keep or change her approach