.
Huge question, Rosie - one that could occupy many PhD theses- and not one cover the same angle.
Mentally we decide yes, no, maybe, perhaps, or to some degree about almost everything. We have evolved to be predisposed to make these assessments because they help us with decisions from the most mundane to the most vital.
A few components affecting opinions and perception of truth.
Sensory perception.
Memory, whether true or false.
Ideas circulating around the globe via the media.
Ideas which confirm or bolster one's sense of identity and belonging.
Being taught something from an early age by one or more people whom we trust.
Emotional predisposition towards something that agrees with our beliefs, values, interests, tastes, plans or hopes.
Evidence based on measured, tested and independently validated research.
Logic/quality of education/thinking skills.
A series of facts which together confirm each other.
Influences of drugs or health conditions which affect mental processes and/or sanity.
"How large is the divide between truth and individual perception of it?"
I don't know how to quantify it.
In psychology, one of the most commonly accepted definitions of sanity is the ability to perceive reality as it is.
It is what Buddhists seek when tuning-in to the senses during meditation.
At a rough and arguable approximation I would say,
to the degree that our perception of the world agrees with our experience of it,
our opinions are probably fairly well grounded in facts.
But the problem is that all of these can be subjective to a greater or lesser degree.
Worse, we often misinterpret things due to flaws in any of the components listed above.
So we need to always remain open to continuous checking.
Thank you for a very thoughtful and thought-provoking analysis in response to my question hartfire. I can always count on you to take me seriously which I almost always am. Actually I did not realize that my question had so many levels until you pointed that out. Which shows the validity of my view that a question is only as good as the answer it attracts. This is a very very very good answer. Thank you for making my question so much better! Happy Friday! :) ((hugs))
Thank you for your reply Sid and Happy Friday! :)