[…] a certain case-form of this compounded adjective [‘ly’] […] was by a change of office converted into a nearly universal adverbial suffix: thus ‘truly’, ‘plentifully’ […] there are noun-forming suffixes, also, which own a like origin. The plainest cases among them, perhaps, are ‘ship’, German ‘shaft’, in ‘lordship’, ‘herrshaft’, and their like […].
- Whitney (1875), a pag.122

[…] suffixes of derivation and inflection are made out of independent words, which, first entering into union with other words by ordinary process of composition, then gradually lose their independent character, and finally come to be, in a more or less mutilated and disguised form, mere subordinate elements, or indicators of relation, in more elaborate structures.
- Whitney (1875), a pag.124

It cannot well take less than generations to pass an element originally independent through those changes of shape and meaning which it must undergo in order to become a suffix. As a set-off against this, to be sure, the results, once attained, are of very wide application.
- Whitney (1875), a pag.129