[DiscourseFan]

So, everyone in the world knows what a circle is, or has a basic idea of a circle: you won't find a person who doesn't recognize one, right? But, there are no circles in the world, empirically--every circle you've ever thought you've seen is actually an ellipse, even the earth itself is oblong, just like all the stars and planetary bodies.

Well, would we call it a mistake if someone described what, empirically, was an ellipse, as a circle? The question itself "What if I'm wrong?" is flawed: we are always already wrong. But it is the wrongness which makes the world, for us; and to the extent our creations are false, to that same extent they are true. So why concern yourself with questions of true or false, right or wrong, Good and Evil? Go out, create your own truth, make the world anew...leave behind all this worrying over nothing.

[selecsosi]

I would argue we utilize symmetry of rotation and balance along with holding a blade at a fixed point (laythe) or rolling hot metal between two bodies (ball bearings), the avantage / creation of that was one of the crucial advances of humanity (being able to make actual circles / cylinders / spheres, since most objects you mentioned are also 3d)

What makes the circle unique (or a copy / scaling of the unit circle) is that it exists defined by a relationship that is true on the euclidean plane, something itself which is ideal, and only exists in our imaginations.

With mater being quantized at some level, we are always approximating, and for my car's sake, things rolling at several thousand rpms, we have some pretty circular things.

[DiscourseFan]

Everyone should read Kant

[Jensson]

> But, there are no circles in the world, empirically

Only if you have an overly strict definition of circle. I don't think it is wrong to call the outline of a ball a circle, or the shape you do if you take an Y shaped object and rotate it along one of those branches, it isn't a perfect circle but it is still a circle.

[mtlmtlmtlmtl]

And crucially, lots of things like the ones you mentioned are often not better approximated by an ellipse than a circle(I realise circles are just a subset of ellipses).

[DiscourseFan]

>I realise circles are just a subset of ellipses

Ah, but in a circle the circumference is always equidistant to the centre, which is never true of an ellipse.

I suppose there is only one circle in the world.

[jibalt]

> Ah, but in a circle the circumference is always equidistant to the centre, which is never true of an ellipse.

It's never true of an ellipse that isn't a circle. i.e., this is a--ahem--circular argument.

[DiscourseFan]

You can't just decide that the circle is contained in the set of all ellipses. Anyway its a philosophical argument, you can't "prove" mathematically that circles are ellipses or vica versa.

Why do circles need to be ellipses anyway, why can't they be absolutely different? If they were absolutely different, then circles would be purely ideal, and yet an organizing principle (or as the say in Greek, an ἀρχιτεκτονική, from when we receive the word architecture). The only way to understand this, ontologically, is if we take the world to be in a constant tension with the "earth," as Heidegger puts it (cf. The Origin of the Work of Art), the thing in which the "rifts," which is the actual discourse of idealism, come about.

You know, I thought about it for a moment, and I don't think the visual circle is even universal. The schema of the circle may be, but the circle itself never appears. See this article below[0].

[0]https://en.wikipedia.org/wiki/Molyneux's_problem

[trealira]

I'm not who you replied to, but the reason circles are ellipses is because the definition of a circle is equivalent to the case of an ellipse where both foci have the same x, y coordinates. You can read about all the definitions of an ellipse on Wikipedia.

https://en.wikipedia.org/wiki/Ellipse

Functionally, they might not be the same if you're programming them. For example, if you have a circle class with members detailing its center and its radius, it might be more efficient to draw an instance of it than an instance of an ellipse class that has two foci members that just happen to have the same values.

[DiscourseFan]

There is only one definition of a circle, and its universal. Anything else is not a circle.

[jibalt]

There is not only one definition of a circle. There are many definitions, all of which are consistent with each other.

[DiscourseFan]

Ok, but there is only one circle

[jibalt]

Obviously not.

[DiscourseFan]

If there were two circles, the second would be isomorphic to the first, therefore, in pure geometry there is only one circle. I suppose by some sort of empirical measure, there would be circles of different sizes, but as we already stated, empirically observed circles are actually ellipses, so in fact there is actually only one circle.