The phrase "determine to" means to make a firm decision to do something. When looking for synonyms for this phrase, one may consider words such as resolve, decide, commit, or pledge. Other possible options include choose, opt, set, or establish. Each of these synonyms carries the sense of making a clear and purposeful choice, as well as a willingness to follow through with the chosen course of action. It's important to consider the nuances of each of these synonyms, as they may have different implications depending on the context in which they are used. Ultimately, selecting the right synonym for "determine to" will depend on the specific purpose and tone of the message being conveyed.