They decided to translate cantus as “chant”, but “song” wouldn't have been wrong. At any rate cantus doesn't mean Gregorian, in the IGMR / GIRM.

The trouble is, CBW3 is out of print, and the successor Music for Catholic Worship has been coming “soon” for the better part of a decade.

Andrew Malton is correct. That’s what cantus means.

The USCCB staff clarified back some fifteen years ago that "cantus" being translated as "chant" does not mean "chant" in a restrictive English sense, but in terms of meaning is equivalent to "song". It was one of the examples where the translation relied on the crutch of friendly cognates without considering meaning. Anyway, if "chant" were to be interpreted in a restrictive sense, you couldn't do polyphonic propers either.

It's all water long under the bridge, and I would not recommend anyone in parish ministry trying to play clever with that choice of translation as if it were a silver bullet to support their goal.

PS: from page 2 of the January 2012 USCCB Divine Worship newsletter, in which the Secretariat for Divine Worship directly addressed the question:

What the periti of V2 might have thought they were getting was a mandate for a Missa Cantata. But since it was an unfunded mandate, it didn't happen, and the Low-Mass-with-hymns paradigm prevailed instead.

The other big (probably even bigger) dog that didn't bark was that few bishops were willing make normatively typical on at least Sundays and days of precept (1) the chanting of the dialogues and orations by the members of their presbyterates, and (2) the singing of the Ordinary.

Cart vs horse placement issues.

Then again, by the time the new missal rolled out, bishops and pastors were fighting a rear-guard action to stanch the hemorrhaging of faithful from regular appearance in the pews after Humanae Vitae.

I will accept that “chant” can be translated in a broader sense (“chanter” is “to sing” in French, for instance). That said, there’s only one way to interpret “chant” in the first three options. We don’t refer to the “songs” in the Graduale Romanum or simplex.

The whole “option four is a loophole so we can do whatever the heck we want” is a despicable interpretation of the rubrics.

For starters (and while I acknowledge this is debated) the options appear to read in a hierarchical sense, if properly contextualized.

Let’s think: SC specifically mandated that Gregorian Chant be retained in the new rite of Mass. MS then specified that the books of chant (yes, chant) were to be updated for the new rite of Mass. Then the rubrics specifically mention chanting first from the Graduale Romanum, and if not that, then the simplex, and if not that, then another collection of antiphons and psalms approved by the local ordinary, and then, if none of those conditions or met, another chant. This is clearly a reductive set of rubrics which stray further and further from the council’s stated ideal, and from liturgical precedence.

Think about it: the old rite entirely consisted of these chants, and then the council states, “we need to keep all this stuff” (and polyphony) and then the first rubric is to “keep doing the same stuff”. This is very straightforward. And if you don’t do the stuff, do the simpler version of the stuff. And if you don’t do that stuff, do other stuff that is derivative of it.

So to then read rubric 4 as wide as a barn door and to drive a tractor clear through it and then entirely ignore ALL of liturgical precedence and tradition is to completely rip the rubric out of context and tradition. (And this is to speak only of the Roman Rite, not of any of the other ancient and apostolic rites which also all incorporate chanted antiphons.)

The Simplex exists. The Graduale Romanum is recommended by name multiple times. It was even revised and recast as the Gregorian Missal (only in 2012!) to fulfill the mandate that things were to be revised to suit the new calendar and form…

And let’s look at polyphony which flowed from Gregorian chant. What does it set? The antiphons in s a special sacral idiom. This is also recommended. (Along with organ)

Now let’s look at the average, suburban NO Mass. No propers, no organ, no chant, no polyphony.

And people HONESTLY dare—based on the liberal reading of option 4 alone—that this is in any way fully compliant with the wishes of the council? (And even funnier: that it’s the ‘unique’ expression of the ‘Roman Rite’?!) (And I forgot to add, all the while also ignoring the propers right in the altar missal itself!)

I. Just. Don’t. Buy. It.

Years ago, in the early days of the PrayTell blog, they published the minutes of the meetings of the liturgical committee at St. John's Abbey from the mid 60s. It was very illuminating. They presumed that Sung Mass=Gregorian chant, and since there were not any vernacular versions of the traditional chant available they decided that in implementing the vernacular liturgy they would do what they called "Solemnized Low Mass," which they conceived of as introducing some elements of High Mass (e.g. the singing of the Sanctus) into Low Mass. They seem to have thought that once music was available they would shift to a vernacular High Mass, but that never seemed to happen. They seem to have come to prefer the "simplicity" of the Solemnized Low Mass. Reading this back then was a real revelation to me in coming to understand how we ended up where we did.

By far my favorite blog series. It’s A+ stuff.

I documented some of it here:
https://forum.musicasacra.com/forum/discussion/11338/the-most-interesting-blog-post-series-of-2014-from-pray-tell-blog-collegeville-archives-from-1960s

Thank you all for your replies. It's been an interesting discussion.

I *could* buy into the word "chant" being used in the non-restrictive sense except for two things:

1. What ServiamScores talks about in how the Graduale Romanum and the Simplex are referred to.

2. If we didn't have this random, solitary use of the word "hymn" when referring to post-communion music, which now I'm wondering is a translation problem or an intentional word choice. Why are they making that distinction? It would be a place where there is no prescribed text, so if that was an intention word choice it makes sense that hymn would be used there.

So my next question is: what is the difference between the different musical forms. A psalm is obvious, but what's the different between a song and a hymn?

but what's the different between a song and a hymn?

Easy songs are found in books with Hymn written on the cover and Hymns are found in Liturgical books including the Kyriale (Angelic Hymn), Graduale, Antiphonale, Processionale, and Hymnarium.

As @Xopheros notes above, the problem is that historically Hymn referred to a Liturgical piece of music, such as the Gloria (Angelic Hymn), Sequence Hymn, Prose Hymn, Processional Hymn, and the Divine Office Hymn.
Other religious but not Liturgical music was just a Song or a Carol (Carols are not just for Christmas).

Now most people refer to any metrical text with a religious theme as a Hymn, including former songs, carols and metrical translations of true Hymns.

So in short the meaning of hymn varies with the context both here and almost anywhere else.

"song"/"cantus-canticum" is simply the broadest category of vocalized music. Psalm, canticle, poem/carmen, and hymn are, as it were, lesser-included subcategories. There's simply no official basis for assuming a restrictive meaning in the context of the 2011 Missal. The text won't credibly bear the function of a silver bullet.

Paraphrasing a post by Dr. Paul Ford from several years ago:
The hymn after Communion as found in the Graduale Simplex, 465–474, is one of these: the Te Deum, the Te Decet Laus, and the Te Laudamus Domine.
This is why, in this particular instance, the word "hymn" is used. There was a rubric in the 1967 revision of the missal regarding this "hymn," but it is not found in the New Order of the Mass. One wonders why. These would be some much superior to the syrupy "meditations" that disfigure the mass in some places.

Except that it's no such thing. That's just reading something into that's not intended.

Yes, but all other things being equal, which they often aren't in reality, and the real question is what energy if any bishops and pastors would expend on a durable basis on making them less unequal in practice. Inertia is powerful.

I would say yes, but I would also say that it was primarily Summorum pontificum and the effect it had on parishes in the years following that allowed that to happen at the local level. That is, places where both the old Roman rite and the new rite coexisted in a single parish are much further along in the fluent use of Gregorian chant in the new Mass than parishes where that didn't happen, regardless of how widely available chant resources are online. That is just my impression based on my experiences of singing/playing in parishes in New York and New England (and travel elsewhere).