Old english irregular verbs
You might, then, consider the Old English language as being primitive and inexpressive by contrast with Modern English. Meanwhile a statement using the preterite, such as iċ sang, can mean "I sang" or "I was singing" or "I have sung". (The use of the present for the future is still acceptable in Modern English: for example, it is perfectly OK to say: "I take my driving test on Tuesday.") So a statement using the present tense, such as iċ singe can mean: "I sing", or "I am singing", or "I will sing", or "I will be singing". Each of these tenses therefore has to play several roles.
Old English really only has two tenses: the present and the past (or preterite). However, it was only rarely used to show a continuous or currently happening action, for example, iċ eom singende þone sang ("I am singing the song") it would be much more normal for an Anglo-Saxon to simply say iċ singe þone sang, using the present indicative. The present participle form (in our example singende) is the equivalent of the Modern English present participle (in this case, "singing") It could be used as an adjective to show that someone was doing something, or usually did something, for example se singenda man - "the singing man".
This is sometimes the case even in Modern English, but more so for Old English.
Verbs have to agree with the subject of the sentence in number (singular when the subject of the verb is just one, and plural when the subject of the verb is more than one), and person (I, you, he/she/it).