Full Idea
The sentence X follows logically from the sentences of the class K if and only if every model of the class K is also a model of the sentence X.
Gist of Idea
X follows from sentences K iff every model of K also models X
Source
Alfred Tarski (The Concept of Logical Consequence [1936], p.417)
Book Reference
Tarski,Alfred: 'Logic, Semantics, Meta-mathematics' [Hackett 1956], p.417
A Reaction
[see Idea 13343 for his account of a 'model'] He is offering to define logical consequence in general, but this definition fits what we now call 'semantic consequence', written |=. This it is standard practice to read |= as 'models'.
Related Idea
Idea 13343 A 'model' is a sequence of objects which satisfies a complete set of sentential functions [Tarski]