The basic strength of amines is determined by several factors, including the inductive effect, steric effect, and stabilization of the cation by hydration. However, the basic strength of amines does not depend on the mesomeric effect.

The mesomeric effect, also known as resonance effect, refers to the delocalization of electrons through pi bonds or lone pairs of electrons. This effect can either increase or decrease the basicity of a compound, depending on the direction of electron flow.

In the case of amines, the mesomeric effect does not significantly influence their basic strength. This is because the lone pair of electrons on the nitrogen atom in amines is already involved in resonance with the adjacent carbon atom. This resonance delocalization decreases the availability of the lone pair for protonation, resulting in a weaker basicity.

To understand this further, let's consider the resonance structures of aniline, a commonly known aromatic amine:

Aniline (C6H5NH2) can exist in two resonance forms:

1. The lone pair on nitrogen is delocalized into the aromatic ring, forming a double bond between nitrogen and carbon:
-C6H5-N+=C6H4.-

2. The lone pair on nitrogen is localized on the nitrogen atom, forming a positive charge:
-C6H5-N+H2

In the first resonance form, the nitrogen atom does not have a lone pair available for protonation, making it less basic. In the second resonance form, the presence of a positive charge on nitrogen suggests a higher basicity. However, due to the resonance delocalization, the actual basicity of aniline lies somewhere between the two resonance forms.

Hence, the mesomeric effect does not play a significant role in determining the basic strength of amines. Instead, factors such as the inductive effect (electron-donating or electron-withdrawing groups), steric hindrance, and hydration of the resulting cation are more influential in determining the basicity of amines.