For most verbs you add an ‘ed’ at the end of the word to change it to the past tense - for example, ‘she talks’ becomes ‘she talked’. However, there are some irregular verbs where the ...

writers usually use the past tense close past tenseA ... writers also use the present tense when they are writing about facts, for example, ‘The Earth orbits the Sun’. This fact is unlikely ...

One’s tense will vary depending on what one is trying to convey within their paper or section of their paper. For example, the tense may change between the methods section and the discussion section.