I've come across this phrase quite frequently in philosphical and scientific writings: a difference that makes a difference. It's appealing.
What good is a difference that doesn't make a difference? In fact, is it even really a difference, if nothing about it makes a difference?
These are deep epistemological waters.
I'm not competent to dive into them. I just enjoy pondering Gregory Bateson's definition of information, which seems to apply more generally to other areas (of course, it could be reasonably argued that information is the essence of everything).
Consider the mind-body problem. Or in some religious circles, the mind/soul-body problem. Is there really a dualism here? If so, one would expect that the difference between mind and body, or soul and body, would make a difference.
Question is, what difference does the supposed difference make?
People have tried for many centuries to definitively answer this question. Not much, if any, progress has been made. In fact, as noted in a previous post, neuroscientific research has been steadily chipping away at purported reasons for believing that the mind/soul is anything different than what the bodily brain does.
But let's imagine that science is wrong. Each of us does have, or is, an immaterial mind and/or soul in addition to the physical brain.
What difference does this dualistic difference make?
So far, there's no demonstrable convincing evidence of any difference. Meaning, whoever we humans are and whatever we humans do can be understood without invoking the hypothesis of something invisibly immaterial being added onto our evident physicality.
This doesn't prove that an immaterial mind/soul doesn't exist. Just that if it does, there's no evidence of it making any difference to our human lives.
Well, except in this way: believing in the existence of an immaterial mind/soul does indeed make a difference to people who hold that belief. Even though almost certainly it isn't true, truth isn't related to certainty.
For many centuries lots of people were certain that the Sun revolved around the Earth, the Earth was flat, heavier objects fell faster than lighter objects, an ether made possible the transmission of light, creation of life occurred all at once, and other things we now know are false.
Actually, though, these beliefs didn't reflect differences that made a genuine difference in the world. The only difference these beliefs made was in the minds of those who believed in them.
Which, of course, led to secondary effects in the world -- such as the Catholic Church torturing people who doubted the veracity of an Earth-centered cosmos.
In this sense, everything that goes on in the brain makes some sort of difference. It requires some expenditure of neuronal energy, some physical connections between various areas of the brain, and such. But this is a pale reflection of differences which really make a difference.
One reason I've become so enthused about land paddling my longboard (pushing an elongated skateboard with a stick) is how marvelously transparent to differences physical activities are.
When I adjust bolts that determine how easily the board turns from side to side, I feel the difference. When I stand at the top of a hill after loosening the bolts, I know that the board is going to behave differently as I pick up speed. Rolling down the hill, I understand that either I'm going to be able to adjust to the difference I've made to my longboard, or I'm going to have a problem with wheel wobble.
There's little or no ability to hide from the reality of the real world when you're doing something physical. Gravity doesn't lie. Physics doesn't lie. Muscles and balancing ability don't lie. I either can do something on my longboard or I can't.
I'm not able to say to myself, "My soul is able to carve its way on this longboard down a steep hill, even if my body can't." Immaterial entities make no difference to how I'm able to ride differently on my board. Nor do they do so if life as a whole.
You might disagree.
If so, I assume you've got a reason for believing as you do. You must have found evidence that things unseen and unsensed make a difference in this visible sensible world. Well, if this is true, please share that evidence.
A Nobel prize might await. Make me your co-discoverer, and we'll share the prize. Now that would really make a difference in my life.