Deduction Logical proof is called deduction the conclusion

Deduction • Logical proof is called deduction; the conclusion is obtained by deducing it from other statements, called the premises of the argument. The argument is so constructed that if the premises are true the conclusion must also be true. For instance, from the two statements “all men are mortar’ and “Socrates is a man”, we can derive the conclusion “Socrates is mortal”. The example illustrates the emptiness of deduction: the conclusion cannot state more than is said in the premises, it merely makes explicit some consequence which is contained implicitly in the premises. It unwraps, so to speak, the conclusion that was wrapped up in the premises.

Deduction • The value of deduction is grounded in its emptiness. For the very reason that the deduction does not add anything to the premises, it may always be applied without a risk of leading to a failure. More precisely speaking, the conclusion is no less reliable than the premises. It is the logical function of deduction to transfer truth from given statements to other statements— but that is all it can do. It cannot establish synthetic truth unless another synthetic truth is already known.

Deduction • The premises of the example, “all men are mortar* and “Socrates is a man**, are both empirical truths, that is, truths derived from observation. The conclusion “Socrates is mortal’*, consequently, is also an empirical truth, and has no more certainty than the premises. Philosophers have always attempted to find premises of a better kind, which would not be subject to any criticism. Descartes believed that he had an unquestionable truth in his premise “ I doubt**. It was explained above that the term “ I** in this premise can be questioned and that the inference cannot supply absolute certainty. The rationalist, however, will not give up, but will continue to look for unquestionable premises.