An auxiliary proposition is a type of grammatical structure used to add emphasis or additional information to a sentence. There are several synonyms for this term, including auxiliary verb, helping verb, and modal verb. These types of verbs are commonly used in English grammar to indicate tense, aspect, mood, or voice. Examples of auxiliary verbs include "be," "have," and "do," among others. In addition, modal verbs such as "can," "could," "may," and "might" are also considered auxiliary verbs. Understanding the different synonyms for auxiliary proposition can help improve your understanding of English grammar and sentence structure.