In the Vatican II decree Unitatis Redintegratio, or "the Decree of Ecunemism," we see the phrase "imperfect" (non perfecta) used to describe "communion" (communio), as well as the typical phrase, "full communion" (communio plena) and "perfect communion" (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, quas ut damnandas graviter vituperat Apostolus; 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, "full communion" (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 "in Christ"; they are members of his body. But, I simply do not understand how one can be in "partial" (non plena) or "imperfect" (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.
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 "imperfect" or "partial" communion with the Church, the body of Christ?