(By Östen Dahl & Viveka Velupillai): "In English, like virtually all European languages, there is a systematic grammatical distinction between present tenses and past tenses, as in the following sentence pair: (1a) The temperature is below zero right now. (1b) The temperature was below zero yesterday at noon. In (1) the form of the finite verb (in this case, the copula is/was) depends on what time we are talking about – what we may call the topic time (following Klein (1994)): the present form is used if the topic time coincides with the time of speech, and the past form if the topic time precedes the time of speech. This is of course a very rough rule in need of a number of further specifications. As was already noted in the introductory chapter, grammaticalized marking of time in the form of tenses is typically independent of considerations of relevance. The fact that time in (1) is also indicated (and more precisely so) by time adverbials does not make tense marking less necessary. Rather, the presence of a deictic time adverbial such as yesterday renders the use of anything but the simple past tense unacceptable in (1b). ❡
Since it is generally the past tense rather than the present that is overtly marked, we may speak of languages having or not having past marking rather than having a past/non-past distinction. ❡
It is only from a Eurocentric point of view that the marking of the distinction between present and past appears to be a necessary part of grammar. Languages may or may not distinguish (1) grammatically, and there is no clear majority for either alternative."