"Let's say" "Let's pretend" "Let's call"

Question

Worldbuilding, according to most, should not be a What If? site.
However, an increasing number of questions are phrased in a "what if" way, and it's not always easy to discern if they're on-topic (building a fictional world) or what-if (asking what would happen) which is off-topic.

The culprit:

"Let's say..."

Many questions do not seem to be phrased as "in this world", but rather, "if there were a world". Instead of "in my world," it's often "pretend there were a world where..."

Does this constitute What-If? Are these questions on-topic?

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Examples include

• Most effective method of creating fear? "Let's say a psichotic alien race..."
• ... What features would humans gain or lose? "Let's say humans lived in caves..."
• Can a split personality itself have split personalities? "Let's say a person has..."
• Time required for isolated colonists to forget about their origin "Let's say that I have..."

And a notable variant to discuss is "let's call"

• "Let's call them Un, Deux and Trois"
• "Let's call her Star B" etc

Answer 1

This seems to be primarily cases of the questioners being hesitant or diffident in the way they word the concept they are proposing for their question. Perhaps, they're having an attack of, possibly, false modesty or they're uncertain about how to put their question.

Now reading into this hesitancy that this is a way of sneaking those dreaded what-if questions in under radar seems to be, perhaps, a step too far.

For example, if the phrase "Let's say" was replaced by the straight forward "Assume etc etc." then it would be plainly obvious this phrase was the preamble to setting up the proposition upon which the question was based.

This can be best illustrated by taking this quotation and making the appropriate substitutions.

Examples include

Most effective method of creating fear? "***Assume*** a psichotic (sic) alien race..."
... What features would humans gain or lose? "***Assume*** humans lived in caves..."
Can a split personality itself have split personalities? "***Assume*** a person has..."
Time required for isolated colonists to forget about their origin "*Assume* that I have..."

I absolutely agree with SRM that imagination and knowledge [1] are necessary for questions to be on-topic, but also that are answerable. However, commonsense, logic, even educated guesswork, a capacity to reason from a given set of parameters, and all-round problem solving are essential too.

To arrive at a position where "let's say" etc etc phrases in questions are signs of what-if questions is reading to much into what are at base sloppily worded questions by questioners who are most likely lacking in self-confidence.

[1] As much as I hate to say it. Science isn't the be-all and end-all of knowledge. My whole training, education and experience as a scientist are staging a revolt at my having said so. But, yes, there are other kinds of knowledge beyond just the scientific.

Answer 2

To me, any question is on-topic when it asks us to employ our imaginations as much or more as our scientific knowledge.

I use an "alternate situation" litmus test -- there has to be some aspect of the question that is not about the real world/real universe for it to be valid on Worldbuilding. Alternative history is fine -- something changed, and X occurred instead of Y. Alternative physics -- something changed, and now up is down or somesuch. Alternative whatever. But if the question is just about something that could happen in this world ("what if Earth were hit by an asteroid?" for example) then it is off-topic and should move to one of the other Stack Exchanges. "What if Earth were visited by aliens?" is something that could happen, but it is still a valid question because it lies outside the current scientific experience. We are called on to extrapolate beyond available data, not just play out a section of the game tree.