Aiming at the material strength problem often met in practical engineering calculation,discusses the inference process of the Forth Strength Theory and Mohr Strength Theory,introduces some concepts of new strength theory,at the same time,analyzes the different application scope of different strength theory on material mechanics.

After a holistic review of the development of the theories on these two types,this paper analyzes their inferential process from the pragmatic and cognitive perspectives and discusses the similarities and differences between them.

On the basis of a re-interpretation of relevance-theoretic comprehension mechanic,the author holds that the optimal relevance that the translator strives for is dynamic and relative,which is in agreement with the nature of translation,and then tries to re-interpret the mental faculty of the translator in the inferential process of translation.