At common law, rape was defined as sexual intercourse by a male with a female not his wife committed without consent and with substantial force overcoming the victim's utmost physical resistance.
Traditionally, statutes have defined rape as sexual intercourse committed forcibly or by threat of force or as sexual intercourse committed without consent and have retained the gender-specific attribute of the common law.
Many states have extended rape law to other forms of non-forcible, but non-consensual, sexual intercourse; to either party being either gender; and to other sexual acts.
The essential elements of rape are generally: sexual intercourse, force or threat of force, and a lack of consent by the victim
Most jurisdictions still require that the perpetrator accomplish the act with either physical force or threat of physical force.
Some jurisdictions interpret their force requirements as merely being the act of sexual penetration itself. In contrast, others require that the force overcome the victim's resistance.
Even states that require that the victim's resistance be overcome differ as to what constitutes resistance. Some require that the victim physically resist and that the defendant physically overpower the victim. Others allow verbal resistance, e.g., saying "no."
Threat of Force
All jurisdictions also allow a threat of force as an alternative to force.
Most jurisdictions require that the threat prevent the victim from resisting due to a reasonable fear or apprehension regarding the victim's physical safety. Non-physical threats do not constitute rape.
Usually this requires both the subjective test of whether the victim had a sincere fear as well as the objective test of whether the fear was objectively reasonable.
Courts no longer require that the victim "resist to her utmost," only that she not consent.
Some courts view consent as being a communicative act. Thus, consent is given when the victim communicates, verbally or by actions, consent; and consent is revoked when the victim communicates a lack of consent.
Other courts view consent as being a state of mind of the victim. Some of these courts then allow the defendant to argue a mistake of fact defense regarding the victim's lack of consent. Others disallow the defense and thus allow a rape charge even when the defendant believes the victim consented.
Sometimes people cannot legally consent to sex, e.g., due to being too young, mentally handicapped, or intoxicated.