Key principle and Critical Successfactor in a BrainStorm session.

Defer all evaluation of ideas during idea generation. 
Separate the evaluation from the generation.
Most groups don't follow this principle and are less productive. The principle increases the odds that we end up with at least one good idea and don't spend all time in criticizing every idea as we think of it.
Besides it helps the group spirit.

---MartineDevos

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Is this a "principle" or a ProtoPattern?

--DavidHooker
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I've seen thousands of uses. So ProtoPattern is out I think.

I could argue 
'''Here 's why this works''' 
or even '''Here's why you want to be doing this'''.

'''Here's what to do''' is too strong but I think AlexOsborn called PostponeJudgment his most important rule for a good BrainStorm.

It might be fun to write these "things" in PatternForm but there are good books about these good practices (or common sense ? of good habits ?). 

See discussion under WhenToUsePatternForm.

--- MartineDevos

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Sir Karl Popper, following the Dialectic of Socrates and attacking what he called Verificationism, asserted that in science, hypotheses begin from unfounded conjecture, to be subjected to Critical Preference and then Reality Testing thereafter, never a'priori. 

-- Aaron Agassi   FoolQuest.com