-mAktA and -DIr are not tense markers but they immediately follow the chapters on tense so that they can be discussed in relation to the tense markers. -DIr can be attached to nouns and verbs and expresses two meanings. One is fact (gerçek). The other one is guess (tahmin). We can attribute these meanings to the sentences depending on their context of utterance. In some cases, when the context is not known, the sentences can be ambiguous. For example, Türkiye'nin başkenti Ankara'dır can mean ‘I guess, it is Ankara.’ Or it can mean ‘It is a well-known fact that it is Ankara.’

Now look at these sentences:

1. Tavuk iki ayaklı bir hayvandır.

2. Dünya yuvarlaktır.

We know that a chicken has two legs, so we can easily say that -DIr in these sentences expresses a fact. But if we were talking about an animal that we were not that familiar with, we could have the guess interpretation as well. The same is true for the other sentence. Due to our knowledge about the physical properties of the earth, we know that the sentence expresses a fact. If we were talking about a planet that we were not familiar with, the same sentence could have had a guess interpretation.