d is capable of producing.

I must now beg leave to stop one moment to consider the perplexities
attending the origin of languages. I might here barely cite or repeat
the researches made, in relation to this question, by the Abbe de
Condillac, which all fully confirm my system, and perhaps even
suggested to me the first idea of it. But, as the manner, in which the
philosopher resolves the difficulties of his own starting, concerning
the origin of arbitrary signs, shows that he supposes, what I doubt,
namely a kind of society already established among the inventors of
languages; I think it my duty, at the same time that I refer to his
reflections, to give my own, in order to expose the same difficulties
in a light suitable to my subject. The first that offers is how
languages could become necessary; for as there was no correspondence
between men, nor the least necessity for any, there is no conceiving
the necessity of this invention, nor the possibility of it, if it was
not indispensable. I might say, with many others, that languages are
the fruit of the domestic intercourse between fathers, mothers, and
children: but this, besides its not answering any difficulties, would
be committing the same fault with those, who reasoning on the state of
nature, transfer to it ideas collected in society, always consider
families as living together under one roof, and their members as
observing among themselves an union, equally intimate and permanent
with that which we see exist in a civil state, where so many common
interests conspire to unite them; whereas in this primitive state, as
there were neither houses nor cabins, nor any kind of property, every
one took up his lodging at random, and seldom continued above one
night in the same place; males and females united without any
premeditated design, as chance, occasion, or desire brought them
together, nor had they any great occasion for language to make known
their thoughts to each other. They parted with the same ease. The
mother suckled her children, when just born, for her own sake; but
afterwards out of love and affection to them, when habit and custom
had made them dear to her; but they no sooner gained strength enough
to run about in quest of food than they separated even from her of
their own accord; and as they scarce had any other method of not
losing each other, than that of remaining constantly in each other's
sight, they soon came to such a pass of forgetfulness, as no