The problem of investigating systematically the possible states of aggregation has not yet been attacked. It has been approached here in the hope of getting a deeper insight into the nature of the liquid state. After a discussion of the general methods, a simplified one-dimensional model is introduced. It was possible to find the exact equation of state. However, it turned out that in this case a single (gaseous) state exists. This is due to the presence of aggregates of all sizes. It is found that the existence of at least one condensed state is possible only if the change in free energy that occurs when an atom is added to a large aggregate is higher than the change that occurs in the addition of this atom to a small molecule. No progress could be made in the understanding of the liquid state.
