The symbolism in the novel helps to work out the theme. Such a minor symbol as the repeated allusion to Samson and Delilah reinforces the way Jude's emotional life undermines the realization of his ambitions. Two symbols of major importance are Christminster and the character of Little Father Time. They are useful to discuss, since the first is an instance of a successful symbol and the second an unsuccessful one.
Jude's idea of Christminster permeates not only his thinking but the whole novel. From his first view of it on the horizon to his hearing the sounds of the holiday there coming in his window as he lies on his deathbed, Christminster represents to him all that is desirable in life. It is by this ideal that he measures everything. He encounters evidence in abundance that it is not in fact what he thinks it is in his imagination, but he will not take heed. It finally represents to him literally all that he has left in life. Of course, other characters as well are affected by Jude's idea of the place. It is a successful symbol because it is capable of representing what it is supposed to and it does not call attention to itself as a literary device.
Little Father Time, however, is a different matter. The boy's appearance, his persistent gloom, his oracular tone, his inability ever to respond to anything as a child-all of these call attention to the fact that he is supposed to represent something. And Hardy makes the child carry more meaning than he is naturally able to. He is fate, of course, but also blighted hopes, failure, change, etc.
The use of irony is of course commonplace in fiction, and a number of effective instances of it in Hardy's novel are to be found. In some of the instances the reader but not the character recognizes the irony; in others, both the reader and the character are aware of it. An example of the first is Jude's occupational choice of ecclesiastical stonework in medieval Gothic style in a time when medievalism in architecture is dying out or the way Arabella alienates Jude by the deception she has used to get him to marry her the first time. An example of the second is Jude's dying in Christminster, the city that has symbolized all his hopes, or the way Arabella's calling on Jude in Aldbrickham in order to reawaken his interest in her helps bring about Sue's giving herself to him.
Irony is particularly appropriate in a novel of tragic intent, in which events do not work out the way the characters expect. Certainly it is appropriate in a novel which has the kind of theme this one does. Struggling to break free of the old, the characters experience the old sufferings and failure nonetheless.