Premise A: The constant c is the speed of light in a perfect or absolute vacuum. Premise B: A perfect or absolute vacuum is a practical impossibility. Conclusion (C): The speed of light in a vacuum is a purely theoretical concept. Note that I am, or consider myself, a philosopher. If I am a physicist, I am at best a classical physicist. I am not asking for highly advanced equations as a response to my argument. I just want to know whether it is valid (i.e., whether the conclusion follows from the premises) and whether it is "true", i.e., whether it is probable that my premises are correct. Thank you.