  where \(\theta\) is quantifier free, one could effectively decide if it was satisfiable in some structure of cardinality \(\kappa\). Ramsey achieved this by showing that one can write down a natural number \(k\) such that for any cardinal \(\kappa \geq k\) this sentence can be satisfied in some structure of cardinality \(\kappa\) just if it can be satisfied in some structure of cardinality \(k\), and to determine this latter just requires checking its satisfiability in one of the finitely many such structures. An important innovation in his proof was the notion of indiscernibles which was to reappear, apparently independently, three decades later in Model Theory. It was subsequently employed in the proof of Michael Morley’s seminal Categoricity Theorem (1965) and later in the proof of the Paris-Harrington Theorem (Paris &amp; Harrington 1977).