Relevant paragraphs from the Herlihy catechism concerning open communion:
- Anyone may receive the Catholic Eucharist provided that they do not explicitly deny the real, substantial, physical presence of Christ (which is the only way it is actually possible to “receive unworthily”. Having doubts about the real presence does not constitute explicit denial). In this way, all are invited to the Lord’s table and all are welcome, including infants, provided that they are able to consume the host respectfully, not spitting it out or performing some other sacrilegious act of desecration.
- Purely as a matter of prudence and to maintain reverence for the sacrament, in ordinary circumstances the Catholic Eucharist should be withheld from the unbaptised; but this is not an inviolable rule, so unbelievers and unbaptised people may be admitted in emergencies (and if some slip through and receive in ordinary times, it’s no grave scandal; not “the end of the world”)
- Catholics may receive the Eucharist in any church where this sacrament is valid. But as a matter of prudence and politeness, they should respect the decision of whatever church they are attending in terms of whether or not to approach the table.
- Catholics may never receive from churches with an invalid Eucharist even in emergencies.
Addendum: Being out of full communion wounds Christian unity, but does not prevent shared sacramental communion. Contrary to current Catholic opinion, sharing the Eucharist is not a statement of full communion in terms of dogmatic belief, although for some reason it is perceived as such at the present time.