Each element that is presented as logically following from some other claims should actually follow from those claims. An argument that does not do this is invalid . An argument that passes this test is valid . Y follows validly from X means that if X is true then Y must be true too. That is, it is logically impossible for X to be true without Y being true too.
Every turkey is a bird.
So some birds are mammals. The premises of the argument are among the things taken for granted. The conclusion of the argument is the point that is at issue. Each element of an argument that is presented as following from some other claims should be likely if those claims are true. Intricate ships are designed by intelligent beings.