The human being is made up of two parts, namely physical and non-physical. Physical part is the one that relates to the physical body, physical senses and dimensions. Non-physical part is the one that comprises of emotional, mental and spiritual bodies. In homeopathy, the constitution of a human being is not with reference to physical body alone. Since homeopathy attaches lot of importance to "mind symptoms", emotional and mental bodies automatically become part of the constitution.
In my opinion, every human being has two constitutions. One is genetic and the other is acquired. Genetic constitution is more or less of a permanent nature whereas the acquired constitution keeps changing. It is affected by everything that we have in the universe be it food, heat, water, air, light, movement of stars, colors or anything. Even the subtle energies around the people we meet in our life also affect us directly or indirectly, emotionally or mentally, less or more. How all these and other factors affect the human being is a lengthy subject by itself, which I shall leave alone for now.
We all know that love and hate have a bearing on our emotional and mental states. Something serious happening at the other corner of the world also stirs our emotional and mental states and generates a thought process. So the things that affect us may be physical, non-physical, measurable, immeasurable, visible, invisible, perceptible or imperceptible. There are innumerable things in the universe that we are not yet aware of even with so much of advancement in science but they affect us one way or the other, directly or indirectly. Such effects may be temporary or permanent in nature. The sum-total of all those effects makes a constitution, which includes physical, emotional, mental and spiritual spheres. As long as a human being is alive, these four layers cannot be detached from each other and cannot be considered in isolation.
With this concept of everything affecting us, if we try to make a list of all such factors, elements and energies, the list may never be complete because we do not know about all of them. In such case it does not seem possible to conclusively attach more importance to one factor and less to another and finally say that such and such thing is the basis of the constitution. Since the factors making up the constitution keep changing and affect the person according to his/her life style, dietary habits, physical, emotional and mental states, there ought to be a change in the resultant constitution and since all the influencing factors are not exactly the same for everyone, every individual has a different constitution. It is the net individual constitution at one point of time that matters and should be considered and treated.