the profession and knowledgeable about it. If his proficiency is not known, then he is liable in all cases, even if he does not go beyond what is needed. For example, a man who knows nothing of surgery performs an operation on someone and opens his abdomen, but is unable to sew it up. There is no doubt that he is liable, for it is unlawful for a person to practise medicine when he does not know it. Just as it is unlawful for a person to issue legal rulings on religious matters without knowledge, so too, in nonreligious matters, he may not undertake something without knowledge. He is therefore liable.

Another example: Suppose someone is asked to circumcise a boy, though he is not a circumciser. Acting on his own judgment, he says, “I want to be excessive in the circumcision, because that is cleaner and better,” and he cuts off the glans along with the foreskin. He is liable, because he is unskilled and has exceeded the proper limit. In fact, he should have been prevented from doing this in the first place, because he is unskilled.

An example of lack of proficiency without exceeding the proper limit is this: if this circumciser circumcises the boy and removes only the foreskin, removing it completely, without leaving any deficiency, but the wound becomes infected and leads to the boy’s death, then he is liable because he is unskilled—not because his hand caused excess harm, but because he is unskilled.

Thus, we may say that liability may arise from lack of proficiency alone, from the harm caused by one’s hand alone, or from both together, according to the examples we have mentioned.

If someone were to say: If you stipulate proficiency, that means medical practice can never advance, for if we say that no one may practise medicine—whether by prescribing medication, performing surgery, or otherwise—unless he is proficient, then when will a person learn?!