Why do We Say in April, on Thursday, at 10 O'Clock? In Search of an Explanation

Why do we say ON Thursday but AT 10 o'clock? Or why do we say AT night but IN the morning? One common answer to such questions is to dismiss the problem: this is the way we speak because this is the way to speak; it is all arbitrary, conventional, idiosyncratic. It is argued that such answers are unilluminating and unsatisfactory. Prepositions such as ON, AT, or IN have their meanings, and the choice between them is motivated by these meanings. There are also certain conventions of use based on cultural expectations; the meanings and the cultural expectations interact and their interaction produces results whose "logic" may be difficult to detect — especially if one looks in the wrong direction, that is, that of "truth conditions" regarding external situations. In fact, however, the problem is not insoluble, and if it is approached with the understanding that meaning is all in the mind and that it is a matter of conceptualizations rather than "truth conditions", the hidden "logic " behind the choice of prepositions for temporal adverbials can be explained. The paper argues, and tries to demonstrate, that the prepositions AT, IN, and ON mean different things, and that the patterns of their use in different types of temporal phrases are determined by their meanings.