When I was five, my mother tried bribing me to behave while she shopped. She handed me a toy plane as we passed through that aisle; I held the package tightly while we checked out. After we got to the car, my childish fingers attacked the plastic and pulled the die-cast jet from its marketing prison. The long, patient wait while Mom finished shopping had paid off. In my hands I held a brand-new replica of a Harrier jet. A brand-new replica Harrier that had one tail fin angled forty-five degrees out of true.

After some crying on my part, we gathered the packaging from the car floor and re-entered the store. One in-kind exchange later, I ripped apart another package only to find that this toy model had the same defect. The problem was not with the individual plane. The problem had occurred at the factory. All of the models had the same mistake. My mother said I should pretend it was turning left.

"All the time?" I wailed.

My mother, unlike my five-year-old self, knew not to take models so seriously. Models are inherently flawed; they are lesser than the original. Regardless, models can still be extremely useful. Newton's model of gravity was enough for the Apollo missions, and what good is a 1:1 scale map?

Understanding that our scientific knowledge is "only" a model is the key to true scientific literacy.
Knowing this tells us that our science has built-in limitations, but that it does resemble reality in very fundamental ways. More importantly,
that understanding gives us permission to use our models when they are useful—and permission to discard them when they no longer meet our needs.

A literate person is not a walking dictionary, but someone who has enough knowledge about the language to be able to read.

Being able to examine our models, critically evaluate them, and even discard them is far more scientifically literate than being able to regurgitate facts for a standardized test.
Surely, a certain basic, fundamental knowledge is vital to avoid having to constantly return to Descartes. But as he found, even then, critical thinking is necessary to verify these fundamental "facts." Ultimately,
our models and descriptions of reality must be subject to two overriding criteria: How useful is this model, and how much does this model resemble our observations?

Scientific literacy requires an understanding that science is only a model. We have to be able to jettison our models when our critical thinking leads us to that conclusion.

Our society has largely lost that understanding. We desire immutable facts and constant certainties.
We want clean, hard edges to our world and our knowledge about that world. Politicians, educators, and business leaders crave quantitative metrics that can be compared, compiled, and correlated.
As agenda-driven pundits have attacked scientific thought, we have countered their extremism with our own. Both attackers and defenders blur the distinctions between theories, facts, and hypotheses.

A scientifically literate society knows none of that is necessary.

The edifice of science is not in danger of crumbling; it is under constant renewal.
Each generation's orthodoxy was the prior's heresy.
Many commonly-accepted "facts"—plate tectonics, quantum mechanics, birds' relation to dinosaurs, the Big Bang, RNA's role in the cell, punctuated equilibrium, global climate change, good and bad cholesterol—were extremely controversial not so long ago.
And the process continues, with ongoing challenges to accepted models both in their details and in their broad brushstrokes.
It is understanding the inherent value of this uncertain interplay that is true scientific literacy. It is knowing that Newton, Galileo, or any of our forebearers were scientifically literate themselves, despite not having all the data that we have today.
It is the difference between reciting spelling words and grokking e.e. cummings and Maya Angelou.