When we say "I can't but agree", we are expressing our strong agreement regarding a particular matter or opinion. However, there are many other ways to convey the same sentiment using different phrases and synonyms. Some alternative phrases that can be used are "I wholeheartedly agree", "I couldn't agree more", or "I am in complete agreement". Another way to express agreement could be by saying "I concur", "I endorse", or "I support". Using these synonyms adds variety to our vocabulary and helps us to convey our message more effectively. Whatever the expression may be, the goal is to convey our agreement with confidence and sincerity.