In The Miracle Worker by William Gibson, Gibson uses symbols to connect the abstract nature of Helen's struggles to the concrete reality of her world. Darkness and light are common symbols in many works because they have deep significance, bridging the gap between what is apparent on the surface where a person can actually see and what a situation really reveals. Similarly, it is Annie Sullivan's ability to "see" what is needed and figuratively "unlock" Helen's mind, and so provide a means of communication, upon which this play revolves. Based on Helen Keller's "miracle" in the form of Annie Sullivan, the play shows how even those who have their sight can lack perceptive skills and good judgment, resulting in poor decision-making (the family has never tried to discipline Helen) and often it requires an external influence or even, as Captain Keller would presume, in this case, interference to make a situation clear.
There are many instances in the play where the audience is encouraged to reflect and envision life in Helen's darkness. One instance when Gibson uses darkness and light symbolically comes right at the beginning of Act I. The play opens during the night and the night symbolizes helplessness, foreshadowing what will follow. There is only a dim lamp light by which to see. This is representative of the situation before Annie arrives. The doctor suggests that the family rests especially as it has been by Helen's bedside during her illness. The fact that people sleep during the night (the darkness) and the family has been deprived of sleep (therefore remaining in the dark without the benefit of restful sleep) is significant. In the real and the symbolic darkness, the doctor and the family cannot begin to understand the significance of recent events or what is about to unfold. There is potential (the light is lit after all, even though it is dim) but it will remain unrealized without Annie's intervention.
Kate tells her husband to "Look" when she realizes that something is wrong with Helen, but notably, Helen does not respond to the light of the lamp (note the symbolism of this) as Kate holds it in front of Helen's face. Light is revelation. It is ironic that Annie, a partially-sighted person herself, is the one who will provide the link between the real darkness which, for Helen, will never change and the whole family's future which will most definitely change as Annie guides Helen and her family towards the light in the form of success.