(just a meme not fact).
This is the Dogma that gave Keynes advantage over Hayek, they were debating apples and oranges. Mises, so elegantly discounted every economic mathematical model proposed for the same reason.

Human Preference is a social science, and Human Preference is key to understanding at what point, to use previous examples, people stop buying corn and start buying grain, and at what point they substitute grain with sorghum, and when do consumers give that up and consume seaweed, - this is why  monopolies are hard to maintain.

How individuals determine value is irrational, (this is as true of 2 year olds as it is of stamp collectors or a gold bug), it is largely circumstantial time and need dependant)  given this as a fact any economic calculation that involved a fixed value (defined by consumer demand) should be considered a stoical science.   (Scientific models are rejected wrongly because opponents add Human Preference to make their argument.)  

Mathematic principles derived from the laws of nature can be defined and are therefore considered science.  Take meteorology for eg.  The principle of air moving from a high pressure to a low pressure is science. There are so many factors like the surface area on all the leaves on the trees the wind moves past, and given that will affect the speed at which the air will travel are not understood this  does not negate the scientific principal. (Given just this one unknown an accurate predictions will always be wrong); and depending on the time, place and circumstances the measurements are taken one may even get the direction of the wind wrong - but the scientific facts the direction of air flow will move from a high to low pressure will always be correct. Likewise It is in this scientific fundamental market principle that supply and demand determine the direction of price, it's just we can't measure it accurately because of human preference, but like meteorology, we know the science behind high and low pressures is sound, we can know the principals behind supply and demand are equally sound.