These words refer to a situation in which the place of one thing is taken by another. Replace is the most informal and most neutral of these words, referring to any simple substitution for whatever reason: She replaced the amber necklace with a string of pearls to see which she liked better. The word is especially used to indicate the substitution of something new or functioning for something old, worn out or lost: an offer to replace the missing volume of the encyclopaedia; replacing the burnt-out light globe; She replaced the old, battered cushions with new ones.

Displace , by contrast, indicates the dislodging or forcible removal of one thing by another, without necessarily suggesting that the first had become unusable or ineffective: republics in which new régimes displace old ones with wearying predictability; the growing number of employees being displaced by computers. Supplant is even more restricted than displace , usually suggesting that the old thing is deliberately uprooted, rendered ineffective or wiped out so that the new thing can take over. This process may be immediate or gradual: Europeans who supplanted the indigenous Indian populations they met with; new models and fashions that vie in the stores to supplant on another.

Supersede is the most formal of these words indicates that a substitution occurs because the new thing is better, more modern or more effective than the old: consumers who have been taught to believe that this year’s models actually supersede those of the year before; economic planning that would slowly supersede older hit-and-miss methods. The word may sometimes suggest mere substitution because of greater authority: case-fire orders that immediately superseded all previous orders to attack.