The source of a grammaticalization path is a certain notion in a certain discourse or syntactic function. Before a language can recruit lexical items and constructions for grammaticalization, it must first possess these sources. The first example here is the relational notion of ‘finish’ applied to a proposition ().

The most productive path of grammaticalization of aspect is fed by verbs designating phases of a situation which take clausal complements, like ‘start’, ‘keep’, ‘cease’. Yucatec and Chinese share this source and thus develop them to aspect markers. German does not have such verbs and consequently does not grammaticalize aspect.

Another example is the local configuration of an object being positioned at the ‘bottom’ of a reference object ().

Languages like Japanese, Turkish, Cabecar and many others recruit relational nouns for the formation of complex adpositions. English, too, has region nouns like top, bottom, front, back and side which function in complex prepositions like on top of, at the bottom of, in front/back of, and also older prepositions originally formed in the same way like beside and inside. This pattern is productive, may provide an inexhaustible source for new adpositions and may thus guarantee typological stability of this subsystem of a language over a long time. There are, however, languages which lack such basic region nouns. Latin and German are among them. Consequently, these languages cannot grammaticalize these to case markers. They take recourse to very heterogeneous sources for the formation of adpositions.