All Toyotas are Japanese cars. Some Japanese cars are made in America. Therefore, some Toyotas are made in America. On the other hand, if we replace x by Toyotas and y by cars and z by Porsches , we get a line of argument leading to a conclusion that is incorrect. All Toyotas are cars.
Some cars are Porsches.
Therefore, some Toyotas are Porsches. What distinguishes a correct pattern from one that is incorrect is that it must always lead to correct conclusions, i.e. conclusions that are true whenever the premises are true. As we will see, this is the defining criterion for what we call deduction . Now, it is noteworthy that there are patterns of reasoning that are sometimes useful but do not satisfy this strict criterion. There is inductive reasoning, abductive reasoning, reasoning by analogy, and so forth.