Sir: David Cohen ("The Bodies in Question", 11 April) is right to be sceptical about the use of human body parts by the sculptor Anthony-Noel Kelly, but I think his blanket dismissal of the use of casts of "found objects" is unjustified.

He notes that the old masters "who risked the law to work from cadavers did so from a humanist impulse to understand life and the body". But the use of casts was also crucial to the development of a humanist art. Artists' studios contained plaster casts of limbs, heads and faces as well an of antique sculpture.

What marked these casts out as specifically "humanist" was that they were casts taken from life. Medieval artists frequently used death masks, particularly for sepulchral monuments. Casts from death masks were sometimes even superimposed on terracotta busts. This is the tradition to which Kelly belongs. Not surprisingly, these artefacts look grimly inert.

In mid-15th century Florence, however, a revolution occurred when life masks started to be used. The art historian John Pope-Hennessey has written that "with the introduction of the life mask there obtrudes into the portrait bust for the first time an interpretative element".

The key example is Antonio Rossellino's bust of the doctor Giovanni Chellini in the Victoria & Albert Museum. Pope-Hennessey concluded that with this bust "Renaissance portraiture acquires a third dimension, a new weight and thoughtfulness". The use of life masks licensed liveliness and vitality in art: it forced the artist to give the depicted body a soul.

This is as true today as it was then. For artists such as Antony Gormley, Marc Quinn and Kiki Smith, the cast from life is not, as David Cohen would have it, "a way to evoke the real without the effort or skill involved in drawing". It is a springboard for the imagination. This is why their best work seems so charged, focused and thoughtfully alive.

JAMES HALL

London SW11