Intentionality is one of the central concepts in phenomenology. In the book two of his famous book, ‘Psychology from an Empirical Standpoint’ Brentano offers a vivid description of his thought on intentionality. Here he introduced the most important and influential doctrine for understanding the fundamental and crucial distinction between psychical and physiological or non-mental phenomena. The whole doctrine is based on the famous Brentanoian concept of the intentional- inexistence of mental or psychic acts. This doctrine has become decisive constituent of psychological phenomena. It is called decisive not only in the context of Brentano, but also in the context of the later phenomenologist, like Husserl. Husserl, one of the followers of Brentano placed it in proper phenomenological map. While investigating psychical (mental) phenomena Brentano discovered that every psychical phenomena is characteristically different from physical phenomena by being intentionally related to some object. He then contended that intentionality is the sufficiently distinguishing feature of all mental phenomena, while no non-mental (i.e. physical) phenomena deserve this peculiarity. Here I just want to point out the fact that helps Brentano to formulate his whole theory of intentionality. All will be discussed elaborately after the discussion of the methodological approach and the source of the thought of Brentano.