My snail travels at a constant speed and will travel the distance of a pencil in 30 seconds. We can measure this snail's speed to be 1 pencil per 30 seconds, or 1/30 p/s, or 30 s/p. We now hold this as a constant.
According to your idea, we can take this to mean that 30 s = 1 p. However, this would assume that 30 s/p = 1, since we multiply each side by p.
30 s/p
30 s/p = 1
30 s = 1 p
And this would also assume that we can have a number in this equation without a type of measurement.
The speed of light is a constant, so we take how long it travels in a certain amount of time. However, this becomes pointless if we say that the speed of light travels this many units in this amount of time, so this unit is this amount of distance vs. time. It basically states the same thing without actually stating how the measurement came about. The truth is, "the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent 1⁄10,000,000 of the distance from the equator to the north pole through Paris", so it holds nothing when being compared to time.
If you really want to go about it this way, then find a way to connect time and space without using a definition that uses circular reasoning. Yes, this means I'm saying that the SI definition uses a circular arguement, but you should be okay with this since it would be a logical fallacy to assume its lacking flaws.
Argumentum ad numerum (argument or appeal to numbers). This fallacy is the attempt to prove something by showing how many people think that it's true. But no matter how many people believe something, that doesn't necessarily make it true or right. Example: "At least 70% of all Americans support restrictions on access to abortions." Well, maybe 70% of Americans are wrong!
Circulus in demonstrando (circular argument). Circular argumentation occurs when someone uses what they are trying to prove as part of the proof of that thing. Here is one of my favorite examples (in pared down form): "Marijuana is illegal in every state in the nation. And we all know that you shouldn't violate the law. Since smoking pot is illegal, you shouldn't smoke pot. And since you shouldn't smoke pot, it is the duty of the government to stop people from smoking it, which is why marijuana is illegal!"
A good summing up statement is, "In other words, they are trying to tell us that X is true because X is true! But they have yet to tell us why it's true."
EDIT:
"The metre is the length of the path traveled by light in vacuum during a time interval of 1⁄299,792,458 of a second. It follows that the speed of light in vacuum is exactly 299,792,458 metres per second. "
And technically, you would be defining speed of light through meters, which pretty much sets us back to sqaure one.
Post has been edited 1 time(s), last time on Jul 27 2008, 5:37 am by A_of-s_t.