dave: i don’t know about spiritual communion. as far as i know, however, even a drop from the chalice or a very small particle of the host would suffice and could be administered under virtually all circumstances. as to the mortal sin part, i think that if the person didn’t know it was a mortal sin, it would not be a mortal sin (at least subjectively). One condition for a sin to be a mortal sin requires “full consent” of the will and if the person didn’t know any better, there would not be full consent of the will. it does raise a very interesting question nonetheless: can one really not recognize that one has committed a mortal sin? perhaps there is always a still, small voice that would always tell one that wrong has been done, no matter how many rationalizations might be used to cover the reality. perhaps. perhaps. in any case the hypothetical individual that you site would have some “time” in purgatory. hope this helps. tom st. martin