There is a lovely tension and ambiguity in the work of Marlene Dumas that makes her images mysterious and worthy of close scrutiny. On the one hand, she seems unsure about painting itself and what images mean in an age saturated with images. She is engaged emotionally and intellectually with the history of the icon and the photograph. She knows how weak and uneasy painting can seem compared with the brash power of photography and film. But paint for her has both a dark frailty and a deeply suggestive force. The emotional density in the images she makes is combined with a sort of helplessness in the face of what she sees and imagines and wishes to create.

The body, the face, the closeup, the iconic, the erotic, the vulnerability and the lure of flesh, the connection between public and private, between dream and vivid reality – these are some of her subjects. At times, she is ready to make an image of stark beauty, fearless and exquisite. At other times, she is prepared to make figures or images that are disturbing and grotesque. She can suggest both innocence and something much shadier. The fascination for the viewer is that these elements seem to merge or move further apart, depending on the day, depending on the light. There is nothing stable about the sort of impact that Dumas’s work can have.

Her statements as a painter have as much to do with dream as with an open watching of the world. Her images often seem to come from the moment before or after something has happened. They can have the effect of blurred photographs. Some of her figures, she has said, “are closer to the world of ghosts and angels, daydreams and nightmares, than to real people from the streets”.

But she also knows about the street. And some of her work, when she deals, say, with fear and confinement, is overtly political. But against this is a purity of vision, an interest in creating pictures that are indeed sharp and disturbing, but also shimmering and painterly, and open to question.

• Marlene Dumas: The Image as Burden opens at Tate Modern, London SE1, on 5 February.