Why can amines act as bases in chemical reactions?

Amines act as bases in chemical reactions due to the presence of a nonbonded electron pair on the nitrogen atom. According to the Brønsted–Lowry definition, a base is defined as a species that has a tendency to accept a proton ($H^{+}$).12

In an amine molecule, the nitrogen atom is bonded to hydrogen atoms or organic groups by three sigma bonds, while also retaining this lone pair of electrons. This nonbonded electron pair allows the amine to accept a proton from acidic molecules, effectively forming a bond with the hydrogen ion. This ability to donate the lone pair to a proton is the fundamental reason amines exhibit basic properties.12