I've noticed, to my annoyance, that the (very a-historical) opinion that there is no such thing as "partial communion" has been reverberating with some increased frequency in some corners of St. Blogs. The purpose, generally, seems to be to suggest that one is either in full union with Rome, or completely outside of the Church. Of course, that is in direct contradiction to the Second Vatican Council's decree on the Church (cf. Lumen Gentium 13, which forms the basis for the Council's impetus for ecumenism: "All men are called to be part of this catholic unity of the people of God which in promoting universal peace presages it. And there belong to or are related to it in various ways, the Catholic faithful, all who believe in Christ, and indeed the whole of mankind, for all men are called by the grace of God to salvation.").

The early Church certainly had a conception of "full" and of "partial" communion.

In his book Corpus Mysticum, Henri Cardinal de Lubac notes, "first of all there was simple communion, which comprised only communion in prayer or at most comunion in the offerings, which entailed admission to the ceremonies of the Church, then, subsequently, full or perfect communion, which in addition consisted of full sacramental reception of the bread of Christ: the sharing in the mysteries or sharing in the bread." (cf. Ambrose, In Lucam, 7, n. 232; Fulgentius, ep. 12, n. 26).

To quote a primary source, St. Augustine, one of the four fathers of the Western Church, writes that the Donatists are "in communion" with the Catholic Church insofar as they agree with the Catholic Church, and "out of communion" with the Catholic Church whereever they disagree with the Catholic Church. Communion with the Church, Augustine teaches, is a spectrum.

Thus, we read in On Baptism, Against the Donatists I:1,
If, therefore, a man who has severed himself from unity wishes to do anything different from that which had been impressed on him while in the state of unity, in this point he does sever himself, and is no longer a part of the united whole; but wherever he desires to conduct himself as is customary in the state of unity, in which he himself learned and received the lessons which he seeks to follow, in these points he remains a member, and is united to the corporate whole.

As you'll find out if you read the whole work, knowingly separating yourself from full communion, Augustine teaches, has eternal consequences. But, separation from full communion still entails partial communion.

So, the next time that you're skipping off to Mass, and a voice from a dark alley calls out, "hey little kid, wanna learn how there's no such thing as partial communion?", make Nancy Reagan proud. Just say no.