Why an application compiled for .NET 3.5 doesn't work when only .NET 4 is installed?
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From a [MSDN page][1], about .NET Framework versions, we know that each version includes all features from the previous versions.

Unlike previous versions of the .NET Framework, the .NET Framework 4 does not allow an application that was built with previous versions of the .NET Framework to migrate forward and run on it if the previous version is not installed

Why is that?


  [1]: http://msdn.microsoft.com/en-us/library/bb822049.aspx