Is there a word/idiom for feigning a belief for the purpose of constructing an argument?

Currently I'm using the phrase "Operating on the premise that". Here's an example:

Operating on the premise that the God depicted in the Old Testament is real, I would provide a sacrificial lamb.

I want to be able to talk about this practice in the abstract.

When I am [new abstraction]ing, I'm able to empathize better and learn from my new frame of mind.

I could establish an acronym (OOPT) and refer to the practice as OOPTing but I feel like logicians or writers must have already solved this, as it's a fundamental behaviour in a lot of practices.

Solution 1:

Let me additionally suggest the term "arguendo": https://en.wikipedia.org/wiki/Arguendo.

You can also simply start your sentence with "Assuming...".

Google Ngram for "arguendo":

Solution 2:

"For argument's sake" is, in my experience, a common idiom and, in fact, has been used as the title of at least one book.

A slight variation is "For the sake of argument" which was addressed in xkcd #1432 (see an explanation here). The title text on the image states in part:

...it's a DEVICE for EXPLORING a PLAUSIBLE REALITY that's not the one we're in, to gain a broader understanding about it.

Additionaly, the Oxford Dictionary offers the following definition for the later (but does not list the former):

As a basis for discussion or reasoning.

According to Google Ngrams, the latter seems to be more common.

The aforementioned comic also makes mention of "playing devil's advocate".