Partial ionization of ethanoic acid:
Ethanoic acid or acetic acid partly dissociates in water and equilibrium is set up among the carboxylic acid (known as the free acid) and the carboxylate ion. An acid that just only partially ionizes in this way is termed a weak acid.
Figure: Partial ionization of ethanoic acid.
If methylamine is dissolved in water, none of the acidic protons are lost at all and the amine behaves like a weak base in place of an acid, and is in equilibrium with the protonated form of it.
Figure: Equilibrium acid-base reaction of methylamine with water.
Methylamine can work as an acid however it has to be treated with a strong base like butyl lithium.