Why are amines basic in nature?

Hint: Amines are bases according to both the Lewis and Bronsted-Lowry theories. The basic chemical structure is that of ammonia ($N{{H}_{3}}$) with a central nitrogen atom as a key atom.

Complete answer:
Amines are formally derivatives of ammonia.It is just like Ammonia.
The basic chemical structure is that of ammonia ($N{{H}_{3}}$) with a central nitrogen atom as a key atom.
Amines are bases according to both the Lewis and Bronsted-Lowry theories.
In organic chemistry,amines are compounds and functional groups that contain a basic nitrogen atom with a lone pair.
Amines can be derived when one or more hydrogen atoms of ammonia molecules are replaced with an alkyl group.
Amines occur in proteins,vitamins,etc
They are also prepared synthetically to make polymers,drugs and dyes.
There are 4 types of amines.
Primary
Secondary
Tertiary
Cyclic.
When one or more hydrogen atoms are replaced by an alkyl group,it is called alkylamines.
When one or more hydrogen atoms are replaced by an aryl group,it is called arylamines.
Lone pair of electrons , present on the nitrogen atom of amines, makes these compounds basic
They are also good nucleophiles.
Basicity of nitrogen increases by any other group which increases the electron density.
The general structure of an amine is nitrogen atom with a lone pair of electrons and three substituents.
Now, amines are lewis bases because they can donate an electron pair, according to Lewis acid-base concept.
${{R}_{3}}N:+{{H}^{+}}\to {{R}_{3}}{{N}^{+}}-H$
As per the Bronsted- Lowry theory bases can accept a proton to form substituted ammonium ions.
${{R}_{3}}N:+{{H}_{2}}O\rightleftarrows {{R}_{3}}{{N}^{+}}-H+O{{H}^{-}}$
Solution -hence, amines are bases according to both lewis and Bronsted-lowry theories.

Note:
The lone pair of electrons on nitrogen atoms of amines make them easily available for protonation.This is the basic cause of the basic nature of amines. The general structure of an amine is nitrogen atom with a lone pair of electrons and three substituents.