For this recipe, we don't recommend substitutions. Fresh herbs impart a green, herby flavor that can be lost with dried herbs. Fresh herbs also contain natural oils that will help to flavor your dishes - crushing or rubbing your herbs together will help release those tasty oils. Particularly in the vinaigrette, you want those herby flavors to really sing - but if you don't have access to fresh herbs and must substitute, it's fine. A good rule of thumb to remember is that 1 tablespoon of fresh herbs is about equal to 1 teaspoon of dried.