The aim of the paper is twofold. The first aim is to analyse aspect in Thai in the framework of the selection-theory approach developed by Breu and Sasse (1991). The second aim is to study all possible co-occurrences of each of the three aspect markers: lw, kamlaŋ, yuu with the four classes of verbs and with the verbs occurring with other strategies within the five classes of states of affairs. It was found that the selectional approach chosen helped explaining the inceptive-stative state of affairs in Thai clearly. It also pointed out that the Thai aspectuality focused on the initial boundary and terminative boundary of the state of affairs. It is here that combinations of the three aspect markers occur. The study shows that they have certain rules of co-occurances.