Why does make throw an error nothing to be done for "all"?

Question

GNU Make

Good evening! Faced such a problem. When I compiled the program through make and all the sources (and objects) were in the same folder (along with the Makefile), then everything was rebuilt well, but as soon as I put the sources into the "sources" folder, make began to give an error:

nothing to be done for "all"

As I understand it, this is due to the fact that the Makefile does not see the time / date of the source changes and thinks that nothing needs to be done.
How can this error be corrected?