August 11, 2016
Dr. Jennifer C van Velkinburgh, Filipodia Publishing
This editing tip is rather simplistic, but it is the cause of much confusion (even among native English speakers).
A general rule of English grammar is that apostrophes are used to indicate possession; for example, for “Filipodia’s editing blog”, the apostrophe indicates the editing blog that Filipodia owns (possesses, or — from an ethical standpoint — takes responsibility for). However, apostrophes are also used in contractions (when two words are combined, such as “do not” being contracted into “don’t” or “we are” being contracted into “we’re”). Such is the case for ‘it’.
The term ‘it’ is a pronoun, meaning that it inherently expresses possession; therefore, no possessive apostrophe is needed and the use of an apostrophe only indicates a contraction.
Simply speaking, the rules are:
Its = possessive, such as “The antibody attached to its antigen.”
It’s = contraction, such as “It’s generally accepted that level of hemoglobin A1c is an adequate measure of glycemia.”