In many jurisdictions, premeditation is the difference between first and second degree murder.
In 2009, in a case named Larry v Branker, Justice Dennis Shedd of the United States Court of Appeals wrote:
"Under North Carolina law, first-degree murder is the unlawful killing of another human being with malice and with premeditation and deliberation. Second-degree murder is the unlawful killing of a human being with malice but without premeditation and deliberation.
"Premeditation means the defendant formed the specific intent to kill the victim for some period of time, however short, before the actual killing. Deliberation means that the intent to kill was formed while defendant was in a cool state of blood and not under the influence of a violent passion suddenly aroused by sufficient provocation. Significantly, however, cool state of blood does not mean an absence of passion and emotion. Rather, under state law, a defendant may deliberate, may premeditate although prompted and to a large extent controlled by passion at the time. Indeed, if the design to kill was formed with deliberation and premeditation, it is immaterial that defendant was in a passion or excited when the design was carried into effect. Thus a killing committed during the course of a quarrel or scuffle may yet constitute first degree murder provided the defendant formed the intent to kill in a cool state of blood before the quarrel or scuffle began and the killing during the quarrel was the product of this earlier formed intent. Additionally, it is sufficient that the processes of premeditation and deliberation occur prior to, and not simultaneously with, the killing."
Similarly, in the Supreme Court of California, Madam Justice Caro Corrigan wrote this in People v Harris:
"A verdict of deliberate and premeditated first degree murder requires more than a showing of intent to kill. Deliberation refers to careful weighing of considerations in forming a course of action; premeditation means thought over in advance.
"The process of premeditation and deliberation does not require any extended period of time. The true test is not the duration of time as much as it is the extent of the reflection. Thoughts may follow each other with great rapidity and cold, calculated judgment may be arrived at quickly."
In Florida, District Court of Appeal of Florida, Justice Douglas Wallace presiding, preferred these words in Berube v State
"Premeditation is the essential element which distinguishes first-degree murder from second-degree murder.
"Premeditation is defined as more than a mere intent to kill; it is a fully formed conscious purpose to kill.
"This purpose to kill may be formed a moment before the act but must exist for a sufficient length of time to permit reflection as to the nature of the act to be committed and the probable result of that act."