Tawhid has four grades. That is, it has one kernel and one kernel of the kernel. And it has the shell and the shell's shell. This means to say that it has two kernels and two shells. Tawhid is like a fresh walnut. Everybody knows the two shells of a walnut as well as its kernel. And the kernel of its kernel is its oil.
The first grade of tawhid is to say "La ilaha il-lal lah" with the tongue only and not to believe it with the heart. So is the tawhid ofmunafiqs .
The second grade is the heart's believing the meaning of thiskalima-i tawhid. This belief is either by seeing, hearing from others, e.g. the belief of us, the ignorant people, or one believes through proofs, with mind's proving. So is the belief of the savants of religion, of the masters of the knowledge of Kalam.