We prove that the satisfaction relation
$\mathcal {N}\models \varphi [\vec a]$ of first-order logic is not absolute between models of set theory having the structure
$\mathcal {N}$ and the formulas
$\varphi $ all in common. Two models of set theory can have the same natural numbers, for example, and the same standard model of arithmetic
$\left \langle {\mathbb N},{+},{\cdot },0,1, <\right \rangle $, yet disagree on their theories of arithmetic truth; two models of set theory can have the same natural numbers and the same arithmetic truths, yet disagree on their truths-about-truth, at any desired level of the iterated truth-predicate hierarchy; two models of set theory can have the same natural numbers and the same reals, yet disagree on projective truth; two models of set theory can have the same
$\left \langle {H}_{\omega _2},{\in }\right \rangle $ or the same rank-initial segment
$\left \langle {V}_\delta ,{\in }\right \rangle $, yet disagree on which assertions are true in these structures.
On the basis of these mathematical results, we argue that a philosophical commitment to the determinateness of the theory of truth for a structure cannot be seen as a consequence solely of the determinateness of the structure in which that truth resides. The determinate nature of arithmetic truth, for example, is not a consequence of the determinate nature of the arithmetic structure
${\mathbb N}=\{\,{0,1,2,\ldots }\,\}$ itself, but rather, we argue, is an additional higher-order commitment requiring its own analysis and justification.