When expressing hypothetical situations or initiating a thought experiment, one commonly uses the phrase "let us suppose". However, there are various alternative synonyms that can be used to express similar ideas. Some of these may include "imagine if", "let's say that" or "for the sake of argument". These phrases allow one to put forth a hypothetical situation to explore an idea or concept further. Another option could be "suppose that" or "let's imagine". These phrases provide the speaker with a range of options to convey the same idea, adding variety to the language and enabling a more complex discussion of any given topic.