O que significa And even then the invention relates to the particular construction or method involved, and not necessarily to the discovery or the idea upon which the invention has been based. ?

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This means “inventions aren’t just ideas or discoveries. They have to have some sort of new device, or a realistic way of being made.”

For example, electricity is not necessarily the invention, but the lightbulb that uses electricity is.
Let’s say that I came up with a brand new, super complicated way of putting on makeup that somehow involves machines. This is not an invention until I create the actual device, or have a realistic plan to create the device. Right now it’s just an idea. Once it is created, that item/device I made is the invention.
A good way to think about it might be: if it’s in your head, it’s just an idea. If you make it, or plan how to make it (and it’s not impossible, it is something you can actually do) then it is an invention.