This method is reasoning by resemblance. It is based on the assumption that if two things resemble each other in certain points, they can be assumed to resemble in all other points and are, therefore, identical in nature. This method was used by Herbert Spencer when he declared that the State is a living organism like animals, because it has certain resemblance with animal organism.
It is a useful method, but must be applied with great caution.
It must be remembered that analogy is not proof and that resemblance is not identity. Analogy becomes misleading, if carried to an extreme. It gives probability, not certainty. Superficial resemblance is not similarity of essentials.