Plainly it is not every error made by a witness which affects his credibility. In each case the trier of fact has to make an evaluation; taking into account such matters as the nature of the contradictions, their number and importance, and their bearing on other parts of the witness's evidence.

The views of the Courts in regard to imprisonment have however undergone modification in the last ten years. Imprisonment is seen more and more as a harsh and drastic punishment to be reserved for callous and impenitent characters. We wish to adopt a more enlightened approach in which the probable effect of incarceration upon the life of the accused person and those near to her is carefully weighed.

The difference between the past and the present is that individual freedom and security no longer fall to be protected solely through the D vehicle of common-law maxims and presumptions which may be altered or repealed by statute, but are now protected by entrenched constitutional provisions which neither the Legislature nor the Executive may abridge. It would accordingly be improper for us to hold constitutional a system which, as Sachs J has noted, confers on creditors the power to consign the person of an impecunious debtor to prison at will and without the interposition at the crucial time of a judicial officer.

My conclusions, on this point, are as follows: when the Law Commission says committal of judgment debtors is an anomaly that cannot be justified and should be abolished; when it is common cause that there is a general international move away from imprisonment for civil debt, of which the present committal proceedings are an adapted relic; when such imprisonment has been abolished in South Africa, save for its contested form as contempt of court in the magistrate's court; when the clauses concerned have already been interpreted by the Courts as restrictively as possible, without their constitutionally offensive core being eviscerated; when other tried and tested methods exist for recovery of debt from those in a position to pay; when the violation of the fundamental right to personal freedom is manifest, and the procedures used must inevitably possess a summary character if they are to be economically worthwhile to the creditor, then the very institution of civil imprisonment, however it may be described and however well directed its procedures might be, in itself must be regarded as highly questionable and not a compelling claimant for survival.

Severability is an important concept in the context of the relations between this Court and Parliament; like 'reading down', it is an instrument of judicial restraint which reduces the danger of producing an overbroad judicial reaction to overbroad legislation.

The bad parts of the statute are not judicially severable, I consider, from the rest of its provisions that deal with imprisonment. Their roots are entangled too tenaciously in the surrounding soil for a clean extraction to be feasible. The conclusion to which I accordingly come is that we are left with no option but to declare those provisions as a whole to be constitutionally invalid on account of their objectionable overbreadth.

If the good is not dependent on the bad and can be separated from it, one gives effect to the good that remains after the separation if it still gives effect to the main objective.