The attack of hydride ions as nucleophiles on electrophilic carbon creates a new C–H bond, therefore the carbon atom undergoes a reduction (gain of bonds to hydrogen). Because of this, this type of reactions is commonly referred to as reductions, even though the mechanism is a nucleophilic addition. Likewise, the hydride delivering agent is more commonly referred to as a hydride reducing agent, or just reducing agent.
Unlike the attack of carbon nucleophiles on a carbonyl carbon, the attack of a hydride ion produces no new C–C bonds and therefore there is no expansion of the carbon chain. Consequently, only primary and secondary alcohols can be made by this approach.