However, the conception we have just been briefly outlining came up against a number of philosophical difficulties.

It is the source of the mysterious consequences and philosophical difficulties in the interpretations of quantum mechanics-topics that continue to be debated even today.

There's a philosophical difficulty here.

Leaving aside certain rare and controversial experiments with artificial and recorded personalities, and the legal and philosophical difficulties arising from them, that was true enough.

(In spite of philosophical difficulties associated with defining viruses as "organisms", it is practical and convenient to regard them as microorganisms in this connection.)

By the same token I don't think he wants to be a scientist as I understand the term until he has settled all the underlying philosophical difficulties.

My aim has been to illuminate some outstanding philosophical difficulties in physics.

But retributivism is not without its own philosophical difficulties.

The process of analogical modelling has philosophical difficulties.

The four friends discuss the philosophical difficulty of knowing exactly what happened.