"He needs, I think, to be able to understand what it is that he is charged with. He needs to be able to plead to the charge and to exercise his right of challenge. He needs to understand generally the nature of the proceeding, namely, that it is an inquiry as to whether he did what he is charged with. He needs to be able to follow the course of the proceedings so as to understand what is going on in court in a general sense, though he need not, of course, understand the purpose of all the various court formalities. He needs to be able to understand, I think, the substantial effect of any evidence that may be given against him; and he needs to be able to make his defence or answer to the charge. Where he has counsel he needs to be able to do this through his counsel by giving any necessary instructions and by letting his counsel know what his version of the facts is and, if necessary, telling the court what it is. He need not, of course, be conversant with court procedure and he need not have the mental capacity to make an able defence; but he must, I think, have sufficient capacity to be able to decide what defence he will rely upon and to make his defence and his version of the facts known to the court and to his counsel, if any."