Given the scarcity of studies explicitly exploring the often tacit assumption that teachers' content knowledge (CK) is pre-requisite of pedagogical content knowledge (PCK), in this study, we draw on Shulman's conceptualization of these notions to examine their relation by content-aligning the CK and PCK measures. Toward this end, we analyzed data from a paper-and-pencil survey gauging primary schoolteachers' CK and PCK on fractions. The data of 373 completed teacher surveys were analyzed using two different complementary approaches, with the one compensating for the limitations of the other: item response theory analysis and statistical implicative analysis. Both analyses suggested that CK could be considered pre-requisite of PCK: when the CK and PCK items were placed on the same item response theory scale in most of the CK-PCK pairs, the PCK items were more difficult than their aligned CK items; additionally, in most of the quasi-implication paths of the statistical implicative analysis, answering the CK items was found to be pre-requisite of answering their aligned PCK items. We discuss the study findings, considering their theoretical, methodological, and practical implications.