C# provides the ref and the out keyword to make arguments to be passed by refere

Question

C# provides the ref and the out keyword to make arguments to be passed by reference. The semantic of the two is very similar. The only difference is in the initialization of the flaged variable:

ref requires the variable to be initialized before passing it to the function, out does not.
out requires the variable to be initialized inside the function, ref does not.
The use cases of these two keywords are also almost the same, and their too frequent usage is I beleive considered a code smell (although there are valid use cases like the TryParse and TryGetValue patterns).

Because of this could someone explain, why there are two very similar tools in C# for so narrow use cases?

Also, on MSDN, it is stated that they have different run-time behavior:

Although the ref and out keywords cause different run-time behavior, they are not considered part of the method signature at compile time.

How is their run-time behavior different?

Conclusion

Both answers looks correct, thank you both. I accepted jmoreno's because it is more explicit.

Explanation / Answer

The MSDN article is subtly incorrect. Instead of "cause different behavior" it should be "requires different behavior".

In particular, the compiler enforces different requirements for the two keywords, even though the same mecanism (IL) is used to enable the behavior.

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