Supposesupposing and what if can all be used to introduce suggestions. Supposing is less common in American English. The verb can be present or past; a past form makes the suggestion sound less definite.
  •             “I don’t have a table cloth.” “Suppose we use a sheet.”
  •             What if we invite your mother next weekend and go away the week after?
  •             What if I came tomorrow instead of this afternoon?
  •             “Daddy, can I watch TV?” “Supposing you did your homework first?”
These expressions can also be used to talk about fears.
  •             “Let’s go swimming.” “Suppose there are sharks?”
  •             “I’m going to climb up there.” “No! What if you slipped?”
             In sentences about the past, past perfect tenses are used to talk about situations that did not occur.
  •             That was very clever, but what if you had slipped?
In our next e-Lesson, we’ll analyze the expression “be supposed to”.