They are not convened for that purpose.
And the pope could have introduced his ideas about divorce, remarriage, and the Eucharist in any way he chose. He happened to do it in a post-synodal document, but not because the synod in some way freed him to do so, or mandated that he do so. It is sometimes suggested that the synod gave him some political cover, but since the idea did not have full-throated support from the synod's participants, the hypothesis seems flimsy.
In short, nothing about the synod compelled, authorized, or permitted the pope to teach as he did. But because of Amoris laetitia, and the controversial synod of 2015, pundits seem now to characterize each synod not as an exchange of ideas, but as a battle for the pope's endorsement.
While the stakes of the pan-Amazonian synod are far lower than they're usually perceived, the stakes of a showdown over a synod in German are much higher than has likely been realized by many Catholics.
The German bishop are planning a two-year "synodal pathway" in the country. The idea is to bring bishops together with lay people, especially those associated with the Central Committee of German Catholics, to pass "binding resolutions," on controversial topics, including sexual morality and clerical leadership.
The planned synod in Germany is not intended to be a conversation. It is intended to redefine the course of Christianity in Germany, even while giving new consideration to long-established points of Christian doctrine.
The Vatican has warned the German bishops not to continue with their plans, noting that a synod of the type planned by the Germans would disrupt the Church's life, and could cause a catastrophe by denying the Church's doctrinal teaching.
But the German bishops, under the leadership of Cardinal Reinhard Marx, have insisted that the synod will proceed, and that the Vatican simply doesn't understand what's at stake.
Marx will meet with Vatican officials this week. The cardinal hopes to persuade the Vatican to allow him to proceed with his plans. He is not in a position to back down, because he has assured the Central Committee of German Catholics, which includes advocates of same-sex marriage, that they will have a deliberative voice in the future of the German Church. Relenting, for Marx, would likely mean losing his support among secular German figures, and, by admitting that the Vatican was right, falling out of favor among the Churchmen who support him.
Cardinal Marx, by some estimates, seems to be playing a kind of ecclesiastical game of chicken with the Vatican, and betting that the pope's Curia will back down before he does.
But if the Vatican does not relent, and the Germans push forward, a great deal is at stake: some experts have suggested that if the Germans proceed with their synodal path in defiance of instructions from Pope Francis and the Vatican, they run the risk of being declared in schism.
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At the moment, Marx seems unintimidated by efforts from two different Vatican offices to rein in Germany's planned synodal process. He might be persuaded, if at all, only by a direct and personal intervention from Pope Francis.
Marx is said to be persuasive with Pope Francis, but sources tell CNA that the pope is growing impatient with the cardinal's approach to the German synod. If Francis has to intervene, and Marx does not accept the pope's direction, the result would be a serious crisis for the Church in Germany.
The situation is still developing.
The pan-Amazonian synod will provide plenty of fodder for debate this autumn. But a serious ecclesiological crisis is unfolding in Germany, and how it will be resolved remains to be seen.