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In this thesis, different systems of quantified modal logic, philosophical theories of possibilism and actualism, and the interaction between these two theories and those systems have been studied.Modal claims, which talk about the world as it could have been and not the world as it is, have by far been under philosophical considerations. Possibilism and actualism, two philosophical theses that have their own point of view towards the world and its objects, analyze these claims and their relevant truth-assigning mechanisms in different ways.On the other hand, over the last century, modal sentences have been formulated, in sentencial and quantified levels, by precise logical systems, called... 

In this investigation has been tried to indagate the Bell’s inequality both theoretically and experimentally. This inequality published by John Bell in 1964 on the EPR argument. In the EPR argument they reasonably deduced that quantum mechanics with the wave function interpretation is incomplete (but proposing correct results), so we must looking for a deterministic and more fundamental and underlying theory than common quantum mechanics, the alternative theory shall contain Reality and Locality assumptions and also could produce current quantum mechanics results. Afterward, scientific probation started for finding a deterministic theory that including hidden variables, infact supplement... 

One of the main arguments between scientific realists and scientific anti-realists is about observability. As a prominent anti-realist, van Fraassen and his theory of constructive empiricism and his views on observability and the use of scientific instruments, have been the subject of many debates. He believes that observation is the sole path to knowledge and observation is only possible through unaided human eye, so seeing through scientific instruments like microscopes does not count as observation, therefore the information gained from these procedures are not necessarily true.This thesis not only examines van Fraassen’s outlooks on the matter, but also examines his opponents’ view and... 

Bhaskar, one of the pioneers of critical realism, pursues two aspects in his presentation in order to solve complex problems in the philosophy of science. The first aspect is highlighting and emphasizing the need of philosophy of science for ontology and paying attention to intransitive objects. The second aspect is acknowledging the social nature of science and the consideration of transitive objects of science as materials of knowledge, or in other words, the material causes of knowledge. What is done in this thesis, after a detailed description of Bhaskar's critical realism, is to examine the three categories of rationality, progress, and scientific realism in his view. With a layered...