"start assuming" is correct and can be used in written English.
You can use it when you want to suggest that somebody should begin to rely on a given assumption. For example: "Let's start assuming that we have enough time to finish the project before the deadline."
After 30, people start assuming you're fine with being on your own, and people start assuming you are picky or not a suitable candidate for someone".
"At some point, everyone's going to start assuming I'm an exhibitionist".
People will have to start assuming that they simply have no privacy.
And we have to start assuming that we could go into one of these longer droughts and maybe start doing some serious conservation and rethinking of agriculture here.
So when the euro comes into being on Jan . 1 , 1999t witl start assuming the same predominance as the dollar.
Scientists have shown that our hands start assuming the necessary configuration as soon as the brain initiates an activity — if not a micromoment earlier.
"Administrators even started assuming that we were in a relationship before we really were," says Kaisha, a program coordinator at the State Department.
But it seems to me that in the decades since we started assuming that every adult was going to work a 40-hour week, a whole lot of things haven't been getting done as well.
So reimbursement for counseling is a good start- assuming we can make sure the counseling is consistently good.
Instead of working to make this country prosper, we've started assuming we're entitled to a share of that prosperity without contributing anything to it.
I got to the point where it just didn't matter to me anymore, so I stopped asking, and started assuming the worst.
