The question is the very idea of Nostratic as a common Proto-language
for a number of families. But what are those families sharing
Nostratic features?

There are obvious similarities in phonetics and morphology between IE
and Semitic (particularly after the Glottalic theory was introduced).
There are also cognates in the vocabulary between IE and Semitic, IE
& Caucasian, IE & Altaic etc.

But still the number of members of the Nostratic macrofamily does not
remain stable. First what we should do, to my mind, is to define
which families are definite relatives. Any opinions?