Substitutional quantification is an alternative to the objectual or referential interpretation of the quantifiers $\forall$ and $\exists$. The truth-conditions for objectual quantifiers are given in terms of Tarskian satisfaction and the variables bound by the quantifiers are understood as ranging over objects. In contrast, the substitutional approach turns on the truth of sentences formed by replacing the variables by certain terms of the language.
The earliest reference I can find to substitutional quantification is Quine's 1969 Ontological Relativity and Other Essays. It mentions nothing about earlier origins of the approach. I am wondering if Quine invented substitutional quantification (or was the first to call it such) and if not, am looking for references to earlier accounts.
Quine allegedly took the notion from Leśniewski (https://plato.stanford.edu/entries/lesniewski/#Qua) but there is some controversy about whether that is the correct interpretation of the latter's work. In 1962, Ruth Barcan Marcus, referring to the substitutional approach, writes: "Recently, one of the fruitful interpretations of quantification seems to have been abandoned or at least submerged" (https://doi.org/10.1080/00201746208601353), suggesting a much early origin of the notion.