Nobody likes to be called a dummy by a dummy.

Why does a semi-circle have to be 180 degrees?

I know that semicircle is defined by Webster as being an 180 degree arc, but, the prefix 'semi-' means partial. Why isn't a 40 degree arc a semicircle? Isn't an 180 degree arc a hemicircle, anyway? What the crap?
Permalink muppet 
August 5th, 2005
No, semi- is a prefix meaning half.

http://en.wiktionary.org/wiki/Semi-

Any further questions?
Permalink Mat Hall 
August 5th, 2005
Any other degree amount other than 180 and it ceases to be a semi-circle, and turns into something else.

I'm not trying to be a prick muppet, but isn't this basic school stuff?
Permalink Cool Dad 
August 5th, 2005
Although there may be some disagreement on the fundamental meaning of "semi-":

http://dictionary.reference.com/search?q=semi

There are uses that imply partial (from the above link, semiconscious). Although personally I would normally assume that semi- implied half.
Permalink Joel Goodwin 
August 5th, 2005
Mat-

'semi-' means partial. It can also mean half but I think that is a more recent usage than the former.
Permalink muppet 
August 5th, 2005
Then why 'hemi-' ?
Permalink muppet 
August 5th, 2005
Cool Dad -

Do you take everything that you've ever learned for granted?
Permalink muppet 
August 5th, 2005
Muppet, I have no idea. I try to learn as much as I can.
Permalink Cool Dad 
August 5th, 2005
Down to the bottom of the barrel now for things to talk about.
Permalink Actively Disengaged 
August 5th, 2005
"It can also mean half but I think that is a more recent usage than the former."

But semi in Latin means half. How much more precedent do you need?

And why Hemi? Because that's a Greek root.

So, any further questions?
Permalink Mat Hall 
August 5th, 2005
Semi comes from the latin for a half.
Hemi comes from the greek for a half.

The use of hemi in hemispherical is probably simply for euphony.
Permalink Simon Lucy 
August 5th, 2005
Bleurgh, you beat me.

118 for 3 at lunch.
Permalink Simon Lucy 
August 5th, 2005
Mat -

Ok so fine you're correct that Latin is pretty much the ultimate precedent, but language evolves, right? Semi- seems to be used much more often to mean "partial" than to mean "half" in contemporary language. 'Semicircle' seems to me like a vestigial tail, or something. Ah well.

Obviously I'm not arguing the current contemporary usage is incorrect, I just wonder why it is what it is.
Permalink muppet 
August 5th, 2005
But muppet doesn't _want_ it to be like that!
Permalink Erik Springelkamp 
August 5th, 2005
I suppose there are language-based arguments one can make, but I suspect the answer to this question is that, one day, a mathematician woke up, saw a 180 degree arc and said, ah, I'm going to call that a semi-circle. He wrote it down, the Great Congregation of Mathematicians of 1729 approved the usage, and thus it became an accepted definition.

You can argue about the origins but I think its probably a mathematical definition. There are examples of poor naming choices in mathematics but, generally, they're not as shit as the stuff that comes out of IT.
Permalink Joel Goodwin 
August 5th, 2005
> The use of hemi in hemispherical is probably simply for euphony.

"Sphere" is from a greek word originally, whereas "circle" is from a latin.
Permalink Christopher Wells 
August 5th, 2005
It's also worth bearing in mind that many mathematical terms have an almost-but-not-quite-equivalent definition to the same word in general use, "line" and "point" being two obvious ones.
Permalink Mat Hall 
August 5th, 2005
Jeez, muppet, do you actually ENJOY being wrong?
Permalink  
August 5th, 2005
He seems to have a problem with mathematical terms (or maths in general); we had a very similar error his understanding of the the word "theorem", which he thought was the same as "theory".
Permalink Mat Hall 
August 5th, 2005
Actually no Mat I know the difference, it was a momentary lapse.

As for enjoying being wrong, how am I wrong? I'm not arguing that the definition is incorrect, only that it seems somewhat open to debate from a purely linguistic standpoint. Do you enjoy trolling without signing a name?
Permalink muppet 
August 5th, 2005
Extending what Christopher Wells said. Dug this usenet post up:

http://groups.google.co.uk/group/sci.math/msg/8afbdd718bdbc713?dmode=source&hl=en

It's considered better to form words from terms with the same root language. Hemi & sphere are both derived from Greek; Semi & circle are from Latin.
Permalink Joel Goodwin 
August 5th, 2005
"As for enjoying being wrong, how am I wrong?"

Because you suggested that any arc can be a semicircle, not just those that are half of a circle, and that they should be called hemicircles. As has been pointed out, "semicircle" is a so-called "undefined term" with a specific meaning, and as "circle" is of Latin origin it takes the Latin prefix.

But apart from that you were completely correct.
Permalink Mat Hall 
August 5th, 2005
No Mat actually I asked a bunch of questions. I don't see any assertions in the OP.
Permalink muppet 
August 5th, 2005
Of course, Heaven and God and Earth forfend that anyone should ask a question on this board, lest the Cavalry of Superior Intellect descend upon them with a mighty vengeance, rending and tearing them limb from figurative limb.
Permalink muppet 
August 5th, 2005
Ok, I'm in a good mood today so I'll give you that. They were silly questions, though...
Permalink Mat Hall 
August 5th, 2005
I apologize profusely with much bowing and scraping and gnashing of teeth for sullying the intellectual sanctity of this holy place with my deliberately silly questions.
Permalink muppet 
August 5th, 2005
Actually you did make an assertion - that the prefix semi- means partial. However, webster has multiple definitions of it, one of them meaning *precisely* half:

Etymology: Middle English, from Latin; akin to Old High German sAmi- half, Greek hEmi-
1 a : precisely half of: (1) : forming a bisection of
Permalink Colm O'Connor 
August 5th, 2005
Colm -

You're right I did make one minor assertion that was completely valid and provable. I apologize for this inaccuracy.
Permalink muppet 
August 5th, 2005
"Of course, Heaven and God and Earth forfend that anyone should ask a question on this board..."

You must admit that in the past you've taken offense at people (normally me) answering questions, claiming it's purely super-inflated ego or smugness that prompted me to answer them.

"...lest the Cavalry of Superior Intellect descend upon them with a mighty vengeance, rending and tearing them limb from figurative limb."

Kind of like that, really. I don't see any rending anywhere, just straightforward answers to your questions.

"deliberately silly questions"

I didn't say they were deliberately silly. I'm trying to avoid assigning motive to your statements, as that way madness lies!
Permalink Mat Hall 
August 5th, 2005
Some words do have more than one meaning, you know. Just giving a heads up ;-)
Permalink Colm O'Connor 
August 5th, 2005
Actually Mat I don't quite remember the thread you're referring to (it simply wasn't that important), but as I dimly recall, you had spent that day and the day before it verbally trouncing about the forum as if you were some sort of fucking Socrates dispensing wisdom to the unwashed masses. The exact confluence of grammar, "tone", and subject matter that created the impression is lost to me now, so I can't defend or explain my comments post-mortem.
Permalink muppet 
August 5th, 2005
Muppet is our resident contrarian.
Permalink KayJay 
August 5th, 2005
this is geekier than usual conversation for this board. well done.
Permalink Kenny 
August 5th, 2005
For a while it was vaguely geeky, but then it descended in to the usual arguments about who's more of an idiot than whom. :¬P
Permalink Mat Hall 
August 5th, 2005
Yeah Mat it's a shame that you have to be so condescending and insulting. You've spoiled a number of really good discussions with your poor, vindictive attitude.
Permalink muppet 
August 5th, 2005
Sorry, I'm not rising to the bait this time.
Permalink Mat Hall 
August 5th, 2005
Hush now.

http://www.bartleby.com/64/C008/047.html

Consider the hemidemisemiquaver of 1/64th note duration AKA the NY second. Is there a 1/128 note duration?.
Permalink trollop 
August 5th, 2005
muppet = troll
Permalink  
August 5th, 2005
It's a shibboleth!
Permalink duh 
August 5th, 2005
I love it when I open up the board in the morning and see stuff like this.
Permalink Jeff Barton 
August 5th, 2005
Muppet said: "Do you take everything that you've ever learned for granted?"

Yes, when it's something that's true *by definition*. If someone tells me Martin Luther King Jr. was black, it's true because it reflects reality. If someone tells me 1+1=2, it's ONLY true because we say it is under the established rules of math. You can argue that 1+1=3, but it's a meaningless argument because the ENTIRE meaning of the equation is a matter of the agreed-upon definitions.

So we call a semicircle a 180-degree continuous arc of a circle. Sure, "semi-" would seem to imply that it could be 62 degrees, just as "circle" could simply imply that it goes "around" something based on the latin root.

At some point you *do* just have to take things for granted, because they *are* granted.
Permalink Tail of the "g" 
August 5th, 2005
Tail -

Certain things are true by virtue of reality, you're right.

In the case of linguistics, though, very few things are set in stone. A word is a symbol which represents another thing, therefore words and their meanings are incredibly malleable. Language is not a discovered artifact, it's a created concept.
Permalink muppet 
August 5th, 2005
In terms of mathematical definitions, though, there is no arguing of semantics. A semi-circle *is* an 180 degree arc, and that's that.
Permalink Mat Hall 
August 5th, 2005
"If someone tells me Martin Luther King Jr. was black, it's true because it reflects reality"

Almost right. But I am in good mode today so I'll let it pass.
Permalink Rick Tang 
August 5th, 2005
Language doesn't change to suit the speaker though but to suit the listener, something that Humpty Dumpty failed to understand as his albumen encountered the green sward.
Permalink Simon Lucy 
August 5th, 2005
Hmmm, well, now I've got a semi...
Permalink Jack of all 
August 5th, 2005
Can we keep cannons from the second civil war out of this?
Permalink a cynic writes... 
August 6th, 2005

This topic was orginally posted to the off-topic forum of the
Joel on Software discussion board.

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