Unitatis Redintegratio: Analogy to describe those in "partial" or "imperfect" communion? In the Vatican II decree Unitatis Redintegratio, or &quot;the Decree of Ecunemism,&quot; we see the phrase &quot;imperfect&quot; (non perfecta) used to describe &quot;communion&quot; (communio), as well as the typical phrase, &quot;full communion&quot; (communio plena) and &quot;perfect communion&quot; (communio perfecta). Imperfect communion would thus be equivalent to non-full or partial communion (communio non plena).
For example, in Unitatis Redintegratio, §3, it is written,

Even in the beginnings of this one and only Church of God there arose certain rifts, which the Apostle strongly condemned. But in subsequent centuries much more serious dissensions made their appearance and quite large communities came to be separated from full communion with the Catholic Church - for which, often enough, men of both sides were to blame. The children who are born into these Communities and who grow up believing in Christ cannot be accused of the sin involved in the separation, and the Catholic Church embraces upon them as brothers, with respect and affection. For men who believe in Christ and have been truly baptized are in communion with the Catholic Church even though this communion is imperfect.
In hac una et unica Dei Ecclesia iam a primordiis scissurae quaedam exortae sunt,[15] quas ut damnandas graviter vituperat Apostolus;[16] posterioribus vero saeculis ampliores natae sunt dissensiones, et Communitates haud exiguae a plena communione Ecclesiae catholicae seiunctae sunt, quandoque non sine hominum utriusque partis culpa. Qui autem nunc in talibus Communitatibus nascuntur et fide Christi imbuuntur, de separationis peccato argui nequeunt, eosque fraterna reverentia et dilectione amplectitur Ecclesia catholica. Hi enim qui in Christum credunt et baptismum rite receperunt, in quadam cum Ecclesia catholica communione, etsi non perfecta, constituuntur.

Therefore, &quot;full communion&quot; (communio plena) is used to describe the state of those who are in the Catholic Church, that is, in the body of Christ. They are incorporated; they are &quot;in Christ&quot;; they are members of his body. But, I simply do not understand how one can be in &quot;partial&quot; (non plena) or &quot;imperfect&quot; (non perfecta) communion with the body of Christ. It seems to me that you are either in Christ's body (full communion, or simply, in communion), or you are not. That is, there's no middle ground.
The Bible says that we Christians are &quot;members of his body&quot; (1 Cor. 12:27), and his &quot;body&quot; is the Church (Col. 1:18).
Question: Using the analogy of a human body to signify the body of Christ, and understanding that Christians are members (body parts) of that body (hands, legs, arms, eyes, etc.), how does one represent (by analogy) those who are in &quot;imperfect&quot; or &quot;partial&quot; communion with the Church, the body of Christ?
Many Catholics, including Joseph Ratzinger (Pope Benedict XVI) find the Mystical Body image to be problematic when discussing such ecumenical issues as you reference here.  This is why Ratzinger pushed for the dogmatic constitution Lumen Gentium to use "People of God" rather than "Body of Christ" in this ecumenical context.  An understanding of the "People of God" was a main topic of Ratzinger's doctoral dissertation.


  Over the years Ratzinger has had a great deal to say about the dogmatic constitution on the Church. In his earliest observations he contends that it did well to subordinate the image of Mystical Body to that of People of God. The Mystical Body paradigm, much in favor under Pius XII, makes it all but impossible to give any ecclesial status to non-Catholics and leads to a false identification of the Church with Christ her Lord. The image of People of God, he contends, is more biblical; it gives scope for recognizing the sins of the Church, and it indicates that the Church is still on pilgrimage under the sign of hope. (Avery Cardinal Dulles, From Ratzinger to Benedict)


This is a common understanding.  Although certain aspects of his ecclesiology may have changed in his later years, the tension between the Mystical Body image and any positive ecclesial status for non-Catholics seems to have remained.