excessively forward; "an assumptive person"; "on a subject like this it would be too assuming for me to decide"; "the duchess would not put up with presumptuous servants"
You use assuming or assuming that when you are considering a possible situation or event, so that you can think about the consequences. `Assuming you're right,' he said, `there's not much I can do about it, is there?'. as'suming that used when talking about an event or situation that might happen, and what you will do if it happens