The seminary as an institution is a direct, dated response to a documented crisis: by the sixteenth century, the training of parish priests across much of Catholic Europe was inconsistent or absent, and reformers on both sides of the confessional divide pointed to poorly educated clergy as a real cause of the Reformation's success.
The Council of Trent addressed this directly in its decree Cum Adolescentium Aetas of 1563, which required every diocese to maintain a seminary, literally a seedbed, where boys could be raised from an early age under supervision and trained specifically for ordained ministry rather than picking up theology informally. Rome had already tested something like the model a decade earlier: the Jesuits founded the Collegium Romanum in 1551 as a school for training priests along disciplined, standardized lines, and Trent's decree generalized that experiment into a universal requirement. The seminary movement gained a second, more practical shape in seventeenth century France, where Jean Jacques Olier founded the Sulpician method at Saint Sulpice in Paris, emphasizing spiritual formation and community life alongside academic study, a model that later spread with French missionary clergy to seminaries across the world. What had been an ad hoc, often absent stage of a priest's life became, after Trent, a fixed and expected institution that Catholic dioceses still maintain.