There is some criticism of this distinction, however, as it confuses “non-theoretical” with “observable”, and likewise “theoretical” with “non-observable”. For example, the term “gene” is theoretical (so a T-term) but it can also be observed (so an O-term). Whether a term is theoretical or not is a semantic matter, because it involves the different ways in which the term gets its meaning (from a theory or from an observation).Whether a term is observable or not is an epistemic matter, because it involves how we can come to know about it. Instrumentalists contend that the distinctions are the same, that we can only come to know about something if we can understand its meaning according to truth-evaluable observations. So in the above example, “gene” is a T-term because, although it is observable, we cannot understand its meaning from observation alone.The explanation of realism and instrumentalism above has provided us the capability to understand the topic with much insight. Now, I switch to under determination thesis. From the above discussion we have the knowledge that instrumentalism is related to pragmatism and this point of view is in contrasts with the scientific realism, which states that theories are often more or less true. Here, I refer to Quine, who said that theories can be underdetermined by all possible observations , and Newton Smith’s, treat this as a threat to realism. He said, realism in his sense has to be rejected if there can be cases of under determination of theories.