Defining conjugate acids and bases

[Tracy Tran 3L]

Why do bases form conjugate acids and acids form conjugate bases? I'm a bit confused on the naming and the reason why they are conjugates of each other.

[Akshat Katoch 2K]

For Bronsted-Lowry:

A conjugate base is formed when an acid donates its H+ ion. Since the now current molecule has given away its H+ it can accept an H+ thus making it a base (A Bronsted base accepts H+).
Example: HPO4 2- becomes PO4 3-

A conjugate acid is formed when a base accepts an H+. Since the molecule now has an "extra" H+ it can then donate that H+ making it an acid (A Bronsted acid donates H+).
Example: OH- becomes H2O

For Lewis Acid/Base:
A Lewis acid has a conjugate base in the products of the reaction.
Lewis base has a conjugate acid in the products of the reaction.

Example:
NH3 + H2O —> NH4+ + OH-

NH3 donates its electron pair to the proton from water to become NH4+, making NH4+ the conjugate acid.
H+ from water accepts the electrons from NH3 making it a Lewis acid and thus making water into OH-, the conjugate base.