The six days of creation recorded in Genesis 1 represent one of the most beautiful and most controversial passages in Scripture. Over the centuries, many interpretations of what the six days mean have been proposed. Here are three common ones:
1. The "ordinary week" interpretation. According to this view the days of Genesis 1 are six, 24-hour days that occur within the space of a week (completed by a literal seventh day of divine rest). While this view historically has been the most common interpretation, there have always been prominent dissenters from this view, including Augustine.
2. The "day-age" interpretation. This view draws on the fact that the Hebrew word for day (yom) also can represent a longer period of time than 24 hours, as it clearly does in Genesis 2:4 ("the day that the Lord God made the earth and the heavens"). According to this view, the days of Genesis 1 represent long periods of time-even the billions of years modern science talks about.
3. The "framework" interpretation. This view holds that the six days of creation are not intended to convey anything in particular about the time or sequence in which God created things. Instead they represent a literary framework into which the events of creation are fitted.
According to the Catechism of the Catholic Church, one must "read the Scripture within the living Tradition of the whole Church" (CCC 112). This means that when interpreting Scripture one must take account of the interpretations offered by the Church Fathers-the source of the Church's Tradition-and by the magisterium, the shepherd and arbiter of the Church's Tradition.
Reading Scripture in this way provides two potential limits that are helpful in narrowing the field of possible interpretations. One is not free to advance a scriptural interpretation that contradicts "the unanimous consent of the Fathers" or contradicts what has been infallibly proposed by the magisterium.
Even when the magisterium has not spoken infallibly, one still must honor what it has said, in keeping with "the authoritativeness of the [magisterium's] interventions, which becomes clear from the nature of the documents, the insistence with which a teaching is repeated, and the very way in which it is expressed" (Congregation for the Doctrine of the Faith, Instruction on the Ecclesial Vocation of the Theologian 24).
Though the majority of Church Fathers took the six days of creation as being six literal days, there was not moral unanimity among them on this question. In addition later Catholic authorities (e.g., Thomas Aquinas; see ST 1:74:2) recognized a diversity of permissible interpretations.
Though the magisterium also has not made any definitive claims regarding the interpretation of the six days, it has given some non-defined statements on this subject. In 1909, the Pontifical Biblical Commission (PBe) issued a series of responses to questions on Genesis 1-3. Among these, the PBC answered the following questions:
"In the interpretation of those passages in the chapters [i.e., Gen. 13] which the Fathers and doctors understood in different manners without proposing anything certain and definite, is it lawful. . . to follow and defend the opinion that commends itself to one?" (Concerning the Historical Character of the First Three Chapters of Genesis [June 30, 1909] 4).
"In the designation and distinction of the six days mentioned in the first chapter of Genesis may the word yom (day) be taken either in the literal sense for the natural day or in an applied sense for a certain space of time, and may this question be the subject of free discussion among exegetes?" (ibid., 8).
The PBC's affirmative replies to both these questions established a significant measure of freedom for the interpretation of the six days. In particular, the answer to the latter question asserted room for the day-age hypothesis.
Further liberty on the question was granted when Pope Pius XII approved a reply from the PBC that effectively nullified the restrictive.aspects of the PBe's 1909 replies, stating: "These replies are in no way a hindrance to further truly scientific examination of these problems in accordance with the results acquired in the last forty years" (Letter to Cardinal Suhard ).
The reply went on to note that "the question of the literary forms of the first eleven chapters of Genesis is far more obscure and complex. These literary forms do not correspond to any of our classical categories and cannot be judged in the light of the Greco-Latin or modern literary types. It is therefore impossible to deny or to affirm their historicity as a whole without unduly applying to them norms of a literary type under which they cannot be classed" (ibid.).
Though there was a great deal of liberty thereby granted to exegetes on how to interpret these chapters of Genesis, Pius XII nevertheless imposed important limits on the types of theories that could be regarded as compatible with the Catholic faith (Humani Generis  36-37). He noted that the great freedom of exegesis permitted in regard to the early chapters of Genesis must be tempered by an awareness that the text is divinely inspired and not on a par with pagan myths (ibid. 38-39).
In recent years the Church has adopted at least the outlines of an official position on the interpretation of the six days. This happened in 1992 with the release of the Catechism of the Catholic Church, which states, "God himself created the visible world in all its richness, diversity, and order. Scripture presents the work of the Creator symbolically as a succession of six days of divine 'work', concluded by the 'rest' of the seventh day" (CCC 337).
The Catechism's statement that "Scripture presents the work of the ~ Creator symbolically as a succession ~ of six days" takes at least a general position on the interpretation of the six days. The "succession of six days" is the means by which Scripture "presents. . . symbolically" the work of the Creator.
(Some have tried to argue that the Catechism means merely that the creation narrative includes a few symbols, but that isn't what it says. Symbolically [Latin, symbolice] is an adverb modifying the verb presents. The resulting symbolic manner of presentation is then specified" as [Latin, tamquam] a succession of six days." The succession of days itself, not just a few items mentioned within the days, is what the Catechism says is symbolic.)
The ordinary week view is at variance with the Catechism's statement because it takes the succession of six days as six literal days, not as a symbolic presentation of what God did.
The day-age view, at least as it is usually presented, also is at variance with the Catechism because it doesn't take the days as symbols. It plays on the fact that the Hebrew word yom can mean either twenty-four hours or a longer period. It simply holds that in this case the word yom is referring to a longer, indefinite period of time. The time period is still a literal one, not a symbol.
That leaves us with the Catechism endorsing some form of symbolic view, such as the framework interpretation mentioned earlier. The succession of six days isn't a set of literal time periods but a symbolic means of presenting what God did in creation. The Catechism doesn't go further than that to tell us the method by which the symbol works, so there is still a lot of room for interpretation.
Different models could be proposed to explain how the six days do their job as a symbol.
It would even be possible to revive a version of the day-age hypothesis by asserting that the word yom here means "day" (the twenty-four hour kind) but that each one of these days symbolizes a longer period of time. That would square with what the Catechism says. It also would square better with Scripture than the dayage theory does.
There's always been a problem with it in that for each day Genesis specifies that "there was evening and there was morning." Evening and morning in that order are the transition points of the day according to the Hebrew reckoning (the Hebrew day starts at sunset). The mention of evening and morning tells you that yom is being used in the twenty-four hour sense, since longer periods are not divided by evening and morning in this way.
While this days-as-symbols-of-ages view better squares with Scripture in this respect, it would still have the other drawbacks of the day-age theory: the sun not being created until the fourth age, after the earth already has dry land, after it has a hydrological cycle, and - most importantly - after it has a day-night cycle.
People in the ancient world knew that daylight comes from the sun, and early writers (e.g., Origen and Augustine) remarked on the fact that the sun was not created until the fourth day, sometimes citing it as a reason not to take these as ordinary, literal days. (It is also worth noting that the day-age theory and its variants would have birds being created on the fifth day—before land animals get created on the sixth-yet science would suggest the order was the reverse: land animals came before birds.)
The creation of the sun on the fourth day is suggestive - as it would have been to the ancient audience - that the succession of days is not intended to be taken as a strict, chronological account and that something else is at work as an ordering principle in the text.
What that might be is not hard to see. For centuries it has been recognized that the six days of creation are divided into two sets of three. In the first set, God divides one thing from another: day from night, waters above from below, and waters below from each other. Classically, this is known as the work of division or distinction.
In the second three days, God goes back over the realms he produced by division and populates or adorns them. He populates the day and night with the sun, moon, and stars. He populates the waters above and below with birds and fish. And lastly he populates the land (between the divided waters) with animals and man. Classically, this is known as the work of adornment.
That this two-fold movement represents the ordering principle of Genesis 1 also is reflected at the beginning and end of the narrative. At the beginning we are told that "the earth was without form and void" (Gen. 1:2). The work of distinction cures the "without form" problem, and the work of adornment cures the "void" (empty) problem. Likewise, at the end of the narrative we are told "the heavens and the earth were finished [i.e., by distinction], and all the host of them [i.e., by adornment]" (2:1).
People have recognized for centuries that this is the ordering principle at work in Genesis 1 (e.g., see Aquinas, ST 1:74:1). The question is whether God actually used that ordering when he created things or whether it is meant figuratively. The creation of the sun after the creation of the day-night cycle would suggest the latter.
The framework interpretation thus accords well with the text of Genesis, with what modern science suggests, and with the Catechism's interpretation of the six days. But it is not the only interpretation compatible with the Catechism, as any interpretation acknowledging the succession of days as a symbol would do the trick.
How much weight should the Catechism's statement be given? The Church does not proclaim it infallibly. While the Catechism contains many individual points of theology that are infallibly defined, the Pope and the bishops did not, in composing the Catechism, choose to make a fresh exercise of the Church's infallibility. The kind of language needed to issue a new definition isn't used. As a result, points that were not defined before the Catechism remain undefined.
It would be fair to say that the Catechism's statement makes the symbolic view the official interpretation of the Catholic Church on the six days. But this does not mean that the Holy See would regard those who take a literal view as sinning (committing the sins of dissent or incredulity).
As noted above, the authority of a teaching "becomes clear from the nature of the documents, the insistence with which a teaching is repeated, and the very way in which it is expressed." The fact it is mentioned in the Catechism indicates that the view is to be taken seriously. But the fact that it is introduced in a magisterial text for the first time here, that it has not been oft-repeated, and that it is not expressed in a forceful way (i.e., "the faithful are obliged to hold") suggest that the Holy See would not have a problem with individual Catholics maintaining a literal interpretation.
Indeed, the recent history of this question has strongly emphasized liberty of interpretation. To introduce the symbolist view in such a casual manner suggests that Rome is wanting to establish more of an official position than it has to this point, yet still not disturb individuals who are attached to the literal view, which heretofore has been both permitted and even historically dominant.
The question of how the six days are to be interpreted should remain an active one in Catholic circles for some time to come.