a biconditional(I think it’s also called a double implication) and circular reasoning?
They are quite different.
A bicondition merely means “A is true if, and only if, B is true” or “A can’t be true without B present”.
A circular reasoning is a little more complicated. It means, “A is true because B is true, which is true because A is true” or “A is justified by B which is justified by A”.
But biconditionals can be the basis for circular reasoning:
- A ↔ B.
- A
=========== - B (modus ponens from 1) and 2))
=========== - A (modus ponens from 1) and 3))
Keep in mind that circular reasoning isn’t necessarily wrong or illogical. It just doesn’t prove anything. You can’t prove A by starting with A as a premise, deduce B, and then based on B, deduce A. It’s just like trying to prove A with the law of identity: Assume A, and then conclude A. That’s perfectly valid logic, but doesn’t prove anything to anyone who doesn’t grant A to begin with.
That’s how I thought of it too. The reason I brought it up is because I saw a very interesting critique of evolution, went something like this:
timcooley.files.wordpress.com/20 … idence.jpg That I think is a biconditional, not circular reasoning, but it certainly appears circular to me.
Similar to the bible example, where the circular reasoning is plainly clear: rationalwiki.org/w/images/7/78/Bible_cycle.jpg
The evolution example is pretty clearly not circular reasoning- What’s fittest is what survives, what survives is what’s fittest. It’s not circular reasoning, it’s a fucking synonym. The biblical example seems circular to me, but it’s all a pretty selectively poor example of how theists think.
That said, ‘survival of the fittest’ is kind of poorly worded. It’s like “Triumph of the successful” or “death of the deceased”.
…not much to add to that.
Frankly Science has become pretty similar to just another Bible, “It’s true because scientists say that scientific experiments say its true”. 
Well, I guess you could say that in an evolutionary context their definitions overlap so much that they do sort of become synonyms and imply each other. And I do agree it’s poorly worded, thanks for the clarification everybody.
It’s not really even Darwinian.´ Darwin would be something like survival of the well-enough adapted. But while the term is somewhat circular - survival of the fittest that is - it is distinct from, say, survival of the blessed. It Points towards effective bodies - and implies incorrectly that the effectiveness of bees vs. Tyranosaurus rex can easily be worked out. But with all it’s faults, it is not simply redundant like the others, especially in a nearly completely monotheist Environment where some people are thanking God, for example, for surviving certain things or there are chosen peoples. I Think Spencer was directly competing with christianity, something I would not say Darwin was doing. Though Darwin did end up using that phrase, oddly enough. Why I don’t know. According to Wikipedia he meant something very like what I would have said is Darwinian above, and I Think that phrase is a poor way to put it.
The phrase “survival of the fittest” is misunderstood because of our modern understanding of “fitness”. We use that word today to mean strength and might, as well as the health one gets from plenty of exercise. One can see how this might be confused with the Darwinian/Spencerian sense of “fitness” because it’s easy to imagine a species surviving due their being stronger or healthier than another, or individuals within a species being stronger or healthier than other individuals within that same species–as if they beat them into extinction with brute force–but what “survival of the fittest” is supposed to means is “survival of those organisms that best fit their environment”–it’s more like a puzzle piece kind of fitting.
But Spencer was, specifically, a kind of social darwinist. He did mean it in the ways modern readers would interpret it. He even thought that evolution had a goal, moving towards the best organisms, more complex one.
A bi-conditional relationship is often that of equivalence… it does not lend itself to circularity very easily.
Like Ucc pointed out… if you are basically saying the same thing in a different way, you’re not being circular… you’re being repetitive.
Take gib’s example:
- A ↔ B
- A
- B
- A
Now imagine B was “batchelor” and A was “single”… and we agreed that if you were any one of those, you’d also necessarily be the other…
So when he says Mad Man P is single… he must concludes that the most attractive man on IMDB is therefore a batchelor… which in turn means that he must therefore also necessarily be single…
Notice he’s not being circular… he’s just shocked by the news and repeating it to himself to make sure it has sunk in.
So he’s responsible for this whole mess! 
lol
I am glad you enjoyed your joke, though I don’t quite get it. In any case the issue around fittest is relates to the doctrine of internal relations, that the relationships a thing/organism has are part of their identity. Some people tend to focus on being these kind of isolated monads whose contain their attributes - neo-classical thinkers are a bit like this, the naive ones. Others get that something like fitness is not contained in the organism but is the Product of the relationships the organism has with its Environment. You can see this play in in the types of organisms, for example, that thrive where there are a lot of humans. Some are pretty tough for their size, like raccoons, but small. Most are small and sneaky, anything from rats to intestinal Worms.
Spencer’s responsible for our confusion over the term “survival of the fittest”.
Yeah, that’s what I was trying to say. The “internal” construal of “fitness” is like health fitness–someone who bulks up or does a lot of cardio or eats well (or combinations thereof). In other words, something a doctor could measure by measure you, not you and your environment.
Then the guy who is really bulked up, after being told he is fit, tries to run a Marathon. He destroys his arches, collapses a fifth of the way there of dehydration,overheating and a heart attack. But I can bench 450 and I have almost no body fat and a high percentage of fast twitch fibers, he says to the ambulance personnel.