Relevancy (or relatedness) has been recognized as a key notion not only in analytical philosophy (which produced the first article on this subject), but also in philosophy of language (pragmatics), logics (relevance and relatedness logics), philosophy of science (with a statistical model of explanation) and in a type of sociological phenomenology. (Phenomenology is a philosophical doctrine teaching that one can arrive at essences, or intelligible structures in consciousness, by a description of subjective or mental processes in which all assumptions about the causes, consequences and wider significance of these processes have been eliminated.) Since the subject of relevancy is itself already being discussed in all these fields of thought, it is not strictly necessary to show how the notion of relevancy is used in philosophical (sub-)disciplines other than ethics. To demonstrate the importance of relevancy it will suffice here to have a general idea of what authors in these other fields of thought have said before on the role of relevancy itself.

The first person ever to write a (published) article on relevancy in particular already compared relevancy with truth and argued that it is the former one, not the latter, which is the 'supreme controlling power in the making of judgments'. ('E was also the first author to lucidly state that 'truth is no excuse for irrelevance'.) All reasoning ultimately depends on the notion of relevance. One does not assert whatever one believes to be true but 'only such a portion of the total truth as one judges to be relevant'.

The first person ever to write a (published) book on relevancy in particular was a phenomenologist who discovered that 'our every action, thought and deed in the lifeworld is guided by and founded on a whole system of relevances'. In 'er system specific types of relevances determine 'finite provinces of meaning'. The crucial significance of relevance in this phenomenological theory is not different from that of a theory in philosophy of science in which statistical relevance is called "the key concept". Both theories will be further outlined in the next division.

The concept of relevance has been said to be 'at the bottom of efforts to solve central philosophical problems and to analyze fundamental concepts'. On this view relevance is not only a fundamental notion for philosophy but also for science and everyday life. It has been mentioned already that linguistic pragmatics recognizes a special maxim of relevance. It has not yet been mentioned, however, that it has also been claimed that this maxim is the most important one of all the maxims that govern our conversation according to the so-called 'cooperation principle'.

We have seen how relevancy is treated as a relational notion in ethical theories, but when just confining oneself to these theories, one might too readily draw the conclusion that all notions of relevancy are of this goal-dependent sort. This is a mistake. It turns out that some relations of relevancy are not believed to exist between entities of a different type (one of them being a goal or something similar), but between entities of the same type (notably when dealing with propositions). In the former case the relation is believed to be an asymmetrical one between a fundament (the element in the domain) and a terminus (the element in the range). In the latter case the relation is symmetrical, and none of the relata would be a focus of relevancy in the sense of a directional entity or relational terminus. Confronted with this discrepancy in the accounts of relevancy, we are forced to search for a possible unity which might underly these dissimilar conceptions. For if there really existed various entirely unconnected forms of relevancy, we might not be justified in simply proceeding on the assumption that the relevancy of discrimination, or, for example, moral relevancy, is of the goal-dependent sort. This justification is needed first.