'Scuse Me While I Swish This Concept
This entry has nothing to do with Jimi Hendrix. Pardon me for a moment while I try to get the concepts of liceity (not licety) and validity straight in my head. I figure if I hear the words in usage a few million times, my reformatted head will figure it out:

From The Society of Saint Pius X - In schism? Without jurisdiction? Invalid and illicit sacraments?

No honest Novus Ordo churchmen - bishops, priests - will go so far as to question the validity of the sacraments and jurisdiction of the Society of Saint Pius X. Even Cardinal Ratzinger does not question the validity. Most will "only" question the liceity.

A clear understanding of the difference between liceity and validity is of fundamental importance here. A licit action means one carried out in accordance with law. The law in question may be natural law, a law revealed by God (such as the obligation to receive baptism), or it may be human legislation, either civil or ecclesiastical, which is in accord with God's law. It follows that an illicit action is objectively immoral, insofar as it violates a just law. A valid action, on the other hand, is one which produces the spiritual or juridical effects which it intends to produce. But it may be either licit or illicit, morally good or morally bad. For instance, a bishop who carries out an episcopal consecration without papal mandate and without beeing in a state of necessity for consecrating bishops, acts illicitly, but validly: he violates a just law, but the man he ordains receives effectively the sacramental powers of a bishop, so that he in turn can ordain true priests, capable of offering the Holy Sacrifice of the Mass. A priest who celebrates Mass while in mortal sin, or without using proper vestments, acts illicitly; but, assuming there are no other defects in the way he offers Mass, it is still valid: the bread and wine he consecrates still truly become the Body and Blood of Christ. In the juridical field, the same principle holds. For instance, a bishop who appoints a certain priest as pastor of a parish knowing that the man is morally or psychologically unfit for the task, will act illicitly, since the appointment will violate canon law. But the appointment will still be valid. In other words, that priest will indeed be the rightful pastor of that parish in question, so that (for instance) the marriages he witnesses there will be true marriages.

From International Catholic University:

2. Validity & Liceity

a. "Validity" has to do with whether or not the sacramental celebration confers grace ex opere operato. A sacramental celebration can be valid or invalid.

b. "Liceity" has to do with whether or not a liturgical practice is in accord with liturgical law. A practice can be either licit or illicit. Making up one's own eucharistic prayer would be illicit.

c. Valid but illicit: ex: a priest making up one's own eucharistic prayer, but using the proper words of institution. Or using leavened rather than unleavened wheat bread.

3. Conditions for Validity: (determined by Holy See)

a. Valid minister: varies depending on sacraments

b. Valid recipient: "eligible receiver." E.g., human being, one baptized for all other sacraments, a male for priestly ordination

c. Intention "to do what the Church does" (not in jest, not mindless, superstitious incantation of magic formulas), e.g., kids in pool, forced ordinations of KGB agents

d. Valid matter: proper sacramental sign, e.g., water for baptism. (Does not fit matrimony & penance perfectly). Remember, significando causans.

e. Valid form: proper words ("this is my body" for Eucharist)

From an Internet Question Box:

Here is what Inestimabile Donum, the Church's most recent major statement on liturgical abuses, states:

"The bread for the celebration of the Eucharist, in accordance with the tradition of the whole Church, must be made solely of wheat, and, in accordance with the tradition proper to the Latin Church, it must be unleavened....No other ingredients are to be added to the wheaten flour and water...." (Inestimabile Donum 8)....

This means that any admixture of any other substance renders the use of the bread for consecration automatically illicit (unlawful). Concerning the issue of what happens to the validity of the consecration (i.e., whether Transubstantiation occurs), here is what Fr. Nicholas Halligan, one of the foremost sacramental theologians in the country, has to say in his manual of sacramental theology:

"...The variety of the wheat or the region of its origin does not affect its validity, but bread made from any other grain is invalid material. Bread made with milk, wine, oil, etc., either entirely or in a notable part, is invalid material. The addition of a condiment, such as salt or sugar, is unlwaful but valid, unless added in a notable quantity. Unbaked dough or dough fried in butter or cooked in water is invalid matter; likewise bread which is corrupted substantially, but not if it has merely begun to corrupt....

"...It is gravely unlawful to consecrate with doubtful matter...." (Nicholas Halligan, The Sacraments and Their Celebration, [New York: Alba House, 1986], 65-66).

Now let's return to jimmyakin.org, where I first encountered these terms:

"Wheat-allergic girl denied Communion", blares the headline at CNN.com.

Actually, technically, that's true.

An unnamed Catholic priest who attempted to celebrate Mass with a rice wafer containing no wheat did indeed deny communion to 8-year-old Haley Waldman, who suffers from celiac disease.

He did so by attempting to celebrate Mass with invalid matter. Because non-wheat grains are invalid matter for the sacrament of the Holy Eucharist, what the girl received was not the Body and Blood of Christ, but an untransformed wafer....

Unfermented grape juice (or "mustum") is a valid substitute, and permission can be obtained from competent church authority for its use in specific circumstances (cf. the "Norms For Use Of Low-Gluten Bread And Mustum"). It's not ordinarily a licit substitute, that is, it isn't normally allowed by church law, and cannot be licitly used without episcopal permission.

But liceity and validity are two different things. Liceity has to do with disciplinary rules established by the Church, which the Church is at liberty to rescind or suspend. Validity has to do with absolute sacramental rules established by divine authority, which the Church has no authority or power to alter or suspend, ever, under any circumstances.

That communion hosts must be unleavened is a matter of discipline, just as that a candidate for Holy Orders must be unmarried is a matter of discipline. The Church can make exceptions to either rule, and indeed in the Catholic Churches of the East those rules don't apply at all. However, that communion hosts must be made of wheat rather than other grains is a matter of sacramental necessity, just as that a candidate for Holy Orders must be a man and not a woman is a matter of sacramental necessity....

I couldn't really find an example of "licit but invalid" (except for a reference to licit drug use in Amsterdam by people with invalid addresses).