(9) The Mystici Corporis reproved both the error of those who teach the impossibility of salvation for those who have only an implicit desire of entering the Church, and the false doctrine of those who claim that men may find salvation equally in every religion. Fenton on EENS

1. Solemn Magisterium: Defined as Church teaching “which is exercised only rarely by formal and authentic definitions of councils or Popes. Its matter comprises dogmatic definitions of ecuмenical councils or Popes teaching "ex cathedra." (Definition from “A Catholic Dictionary”, 1951)
Examples of the Solemn Magisterium would be decisions of any General Councils of the Church, or certain papal encyclicals, such as that defining the Dogma of the Assumption in 1950. Note that it is only in extraordinary circuмstances that the Catholic Church teaches in this manner, which historically has been to combat heresy. For this reason it is sometimes referred to as the “extraordinary magisterium”. For examples of the Solemn Magisterium, here is a list of all solemn teaching during the first 7 centuries of the Catholic Church:Here we can clearly see that in the first 7 centuries of the Church, the Solemn Magisterium was not used often, and very little was solemnly defined. So at least 7 generations of Catholics lived and died during this time with very little solemn teaching by the Church. This is because the majority of what Catholics believe comes from the Ordinary Magisterium of the Church (see next).

So, according to this definition, the Ordinary Magisterium (also referred to as the Universal Ordinary Magisterium) is Church teaching that is continuous and unanimously consented to throughout the Church.

The Ordinary Magisterium is where the majority of Catholic beliefs are taught and learned; through unanimous teaching by preaching, by any written means, the approval of catechisms, the approval of textbooks for use in seminaries, etc.

For example, Arius was considered a heretic before his condemnation at the Council of Nicaea in 325, because the Divinity of Christ (which he denied) was part of the teaching of the Ordinary Magisterium before that Council. The same applies to Nestorius regarding his denial of the Divine Maternity of the Blessed Virgin, where he was later declared a heretic by the Solemn Magisterium at the Council of Ephesus.

Finally, the most frequent reason why the Solemn Magisterium is used is in order to confirm a doctrine which already belongs to the Ordinary Magisterium, but which has come under attack, usually by heretics.