Parables are metaphorical; they are analogies, but never perfect ones. This parable provides an image of four separate vehicles. But if we follow the teaching of the Sutra as a whole, the One Buddha Vehicle is not a separate alternative to other ways; it includes them. Thus, one limitation of this parable is that it suggests that the diverse ways (represented by the three lesser carriages) can be replaced by the One Way (the great carriage). But the overall teaching of the Sutra makes it plain that there are many paths within the Great Path, and the Great Path integrates them all. They are together because they are within the One Vehicle. To understand the many ways as somehow being replaced by the One Way would entail rejecting the ideal of the bodhisattva way (the third carriage), which the Sutra clearly never does.