It is not only legitimate, it is also absolutely necessary to seek to define the precise meaning of texts as produced by their authors--what is called the "literal" meaning. St. Thomas Aquinas had already affirmed the fundamental importance of this sense (S. Th. I, q. 1,a. 10, ad 1).
The literal sense is not to be confused with the "literalist" sense to which fundamentalists are attached. It is not sufficient to translate a text word for word in order to obtain its literal sense. One must understand the text according to the literary conventions of the time. When a text is metaphorical, its literal sense is not that which flows immediately from a word-to-word translation (e.g. "Let your loins be girt": Lk. 12:35), but that which corresponds to the metaphorical use of these terms ("Be ready for action"). When it is a question of a story, the literal sense does not necessarily imply belief that the facts recounted actually took place, for a story need not belong to the genre of history but be instead a work of imaginative fiction.
The literal sense of Scripture is that which has been expressed directly by the inspired human authors. Since it is the fruit of inspiration, this sense is also intended by God, as principal author. One arrives at this sense by means of a careful analysis of the text, within its literary and historical context. The principal task of exegesis is to carry out this analysis, making use of all the resources of literary and historical research, with a view to defining the literal sense of the biblical texts with the greatest possible accuracy (cf. Divino Afflante Spiritu: Ench. Bibl., 550). To this end, the study of ancient literary genres is particularly necessary (ibid. 560).
Does a text have only one literal sense? In general, yes; but there is no question here of a hard and fast rule, and this for two reasons. First, a human author can intend to refer at one and the same time to more than one level of reality. This is in fact normally the case with regard to poetry. Biblical inspiration does not reject this capacity of human psychology and language; the fourth Gospel offers numerous examples of it. Second, even when a human utterance appears to have only one meaning, divine inspiration can guide the expression in such way as to create more than one meaning. This is the case with the saying of Caiaphas in John 11:50: At one and the same time it expresses both an immoral political ploy and a divine revelation. The two aspects belong, both of them, to the literal sense, for they are both made clear by the context. Although this example may be extreme, it remains significant, providing a warning against adopting too narrow a conception of the inspired text's literal sense.
One should be especially attentive to the dynamic aspect of many texts. The meaning of the royal psalms, for example, should not be limited strictly to the historical circumstances of their production. In speaking of the king, the psalmist evokes at one and the same time both the institution as it actually was and an idealized vision of kingship as God intended it to be; in this way the text carries the reader beyond the institution of kingship in its actual historical manifestation. Historical-critical exegesis has too often tended to limit the meaning of texts by tying it too rigidly to precise historical circumstances. It should seek rather to determine the direction of thought expressed by the text; this direction, far from working toward a limitation of meaning, will on the contrary dispose the exegete to perceive extensions of it that are more or less foreseeable in advance.
One branch of modern hermeneutics has stressed that human speech gains an altogether fresh status when put in writing. A written text has the capacity to be placed in new circumstances, which will illuminate it in different ways, adding new meanings to the original sense. This capacity of written texts is especially operative in the case of the biblical writings, recognized as the word of God. Indeed, what encouraged the believing community to preserve these texts was the conviction that they would continue to be bearers of light and life for generations of believers to come. The literal sense is, from the start, open to further developments, which are produced through the "rereading" (relectures) of texts in new contexts.
It does not follow from this that we can attribute to a biblical text whatever meaning we like, interpreting it in a wholly subjective way. On the contrary, one must reject as unauthentic every interpretation alien to the meaning expressed by the human authors in their written text. To admit the possibility of such alien meanings would be equivalent to cutting off the biblical message from its root, which is the word of God in its historical communication; it would also mean opening the door to interpretations of a wildly subjective nature.