Given $\mu , \; \eta :X \rightarrow [0,1]$ we study when the equality $I_{\mu }^{T}=I_{\eta }^{T}$ holds, $T$ being a continuous t-norm, and $I_{\theta }^{T}$ the elemental preorder:\\ \[ I_{\theta }^{T}(y/x) = sup \{z\; ; \; T(\theta (x),z)\leq \theta (y) \}. \]