Direction of logical implication in bijectively related sets

In summary, the conversation discusses a hypothesis about logical implication and a bijection between sets X and A. The speaker proposes that if event ##x_n## happens, it implies that event ##a_n## also happens, and vice versa. However, there are concerns about the accuracy and precision of this definition, as well as potential contradictions with the assumption of causality. The conversation concludes that further clarification and understanding of the concept of causality is necessary before discussing the implications of this hypothesis.
  • #1
entropy1
1,232
72
I have a hypothesis of which I wonder if it's sound. Perhaps you guys can advise me:

Suppose ##x_n\Rightarrow a_n## (logical implication) for some set X and set A. I think we have to assume a bijection.

Then, if ##a_m = False##, ##x_m## should be ##False##, right?

So, in case of a bijection, if ##a_n = True##, it follows ##x_n = True##.

Does that make sense?
 
Last edited:
Physics news on Phys.org
  • #2
I 'm not sure what the ##n## means in ##X_n \implies A_n##. Do you mean ##(\forall x \in X_n)(\forall a \in A_n) x \implies a##, or do you mean ##X## and ##A## are ordered sets of size ##n## where ##x_i \implies a_i##?

A bijection is just a pairing of the elements. It doesn't say anything about how the elements are related. A simple counter example is a bijection for ##X=\{False\}, A=\{True\}.##

1601403486730.png
 
Last edited:
  • Like
Likes Stephen Tashi
  • #3
Jarvis323 said:
I 'm not sure what the ##n## means in ##X_n \implies A_n##. Do you mean ##(\forall x \in X_n)(\forall a \in A_n) x \implies a##, or do you mean ##X## and ##A## are ordered sets of size ##n## where ##x_i \implies a_i##?
What I ment to say is that if event ##x_n## happens, that implies that event ##a_n## happens. That holds for every n.

##x_n \neq x_m## if ##n\neq m##. Same for ##a_n##.

Concluding that if ##a_m## doesn't happen, ##x_m## doesn't happen.

All ##a_n## must have a cause out of set X.

There can only be a single ##x_n## and a single ##a_n## true.

Then ##a_n \Rightarrow x_n##, but it almost seems trivial now. 🤣
 
Last edited:
  • #4
This also assumes that both the as and the xs cover the space of things that can happen. Let x_n be the event that a random integer is n, and a_n be the event that it's either n or -n. Then the implication only goes one way.
 
  • #5
entropy1 said:
Then ##a_n \Rightarrow x_n##, but it almost seems trivial now. 🤣
I think you need an accurate and precise definition to begin with. Having two sets and a bijection doesn't seem to change anything. It's still just 2 events you need to look at. Using logical implication I guess you mean that if ##x## happens then ##a## will happen. And then because there are only two events you think that the reverse must be true as well? But that is not generally true, and the conditions and definitions you've given don't lead to this.

I'm guessing you are assuming that ##a## and ##x## are the only two potential events in the universe, every event must be caused by another event, and every event in the universe must happen.

One scenario is that the universe begins with ##x##, then ##a## happens, then the universe ends. But ##x## had no cause, which violates your assumption. So it must be that ##a## causes ##x##, and you have a loop, with a chicken and egg paradox.
 
Last edited:
  • #6
entropy1 said:
All ##a_n## must have a cause out of set X.
This is not the first time you have talked about 'cause' in relation to implication. There is no point in doing anything else until you have corrected this misunderstanding.
 

FAQ: Direction of logical implication in bijectively related sets

What is the definition of logical implication in bijectively related sets?

Logical implication in bijectively related sets refers to the relationship between two sets where the elements of one set can be mapped to the elements of another set in a one-to-one and onto manner. This means that each element in the first set has a unique corresponding element in the second set, and vice versa.

How does the direction of logical implication affect bijectively related sets?

The direction of logical implication determines which set is the domain and which set is the codomain in the bijective relationship. In a bijective relationship, both sets have the same number of elements and the direction of logical implication does not affect the relationship between the sets.

What is the difference between bijective and injective/ surjective relationships?

In a bijective relationship, the sets are both injective (one-to-one) and surjective (onto). This means that each element in the first set has a unique corresponding element in the second set, and every element in the second set has at least one corresponding element in the first set. In contrast, in an injective relationship, each element in the first set has a unique corresponding element in the second set, but not every element in the second set has a corresponding element in the first set. In a surjective relationship, every element in the second set has at least one corresponding element in the first set, but not every element in the first set has a unique corresponding element in the second set.

How can the direction of logical implication be determined in bijectively related sets?

The direction of logical implication can be determined by looking at the mapping between the two sets. If the mapping is from the first set to the second set, then the direction of logical implication is from the first set to the second set. If the mapping is from the second set to the first set, then the direction of logical implication is from the second set to the first set.

Can two sets be bijectively related if they have different cardinalities?

No, two sets cannot be bijectively related if they have different cardinalities. In a bijective relationship, both sets have the same number of elements, and if the cardinalities are different, then there will be elements in one set that do not have a corresponding element in the other set, making it impossible for the relationship to be bijective.

Back
Top