Final answer:
Two ways to thicken a sauce are reducing the sauce and increasing the cooking temperature.
Step-by-step explanation:
There are several ways to thicken a sauce without using a thickening agent.
1. Reduce the sauce: Simmering the sauce for a longer period of time allows the liquid to evaporate, resulting in a thicker consistency. This works especially well for sauces that contain a high water content.
2. Increase the cooking temperature: By raising the heat, you can accelerate the evaporation process and reduce the sauce to a thicker consistency.
Adding more water or mixing in vinegar would actually have the opposite effect and dilute the sauce, so they are not effective ways to thicken a sauce.