The term 'mute of malice' refers to a defendant who is wilfully choosing not to speak rather than one who is unable to speak through some form of physical or psychological problem.

Mute of malice is one of three special pleas in the UK, the others being autrefois acquit and autrefois convict (previously acquitted and previously convicted respectively). In cases where the defendant is suspected of being mute of malice, a pre-trial hearing will take place to determine the matter. If they are found to be so, a not guilty plea may subsequently be entered on the defendant's behalf.

Knowing whether one's actions are legally wrong, and suffering from a disease of the mind, relate to the defence of Not Guilty by Reason of Insanity (NGRI), the McNaughton Rules. This is defined as the defendant showing a 'defect of reason, caused by disease of the mind, so as not to know the nature of the act, or if they did know it to not know that it was (legally) wrong.'

If the defendant was not intending to harm others then this may be considered by the specific charge (e.g. arson with intent to endanger life vs arson being reckless as to whether life is endangered).