A ruling handed down this week by the US Trademark and Patent Office (USTPO) says that machines can't be listed as inventors on US patent applications.

This follows the same conclusions earlier this year for UK patent applications and for European patent applications.

There are some fascinating philosophical and lexical questions. After all, what is an "inventor"? If a machine achieves the kind of result that was previously only achievable by a human, does that mean it hasn't invented? No doubt PhD theses will be written on this topic.

There are also commercial issues at play here - does the requirement to list a human inventor mean it's harder to disguise the source of an invention and therefore harder to suppress assumptions of ownership?

And then, as always, there are political issues, not least Article 1 of the US Constitution which gives Congress the power, among other things, to give exclusive rights to "inventors".

Of course, whether or not machines will eventually qualify as potential inventors at some point in the future, this week's ruling is unlikely to stunt the seemingly exponential rise of artificial intelligence.