Name _______________________________________

Lesson 28 Forms of the prefixes ob and sub


ob + struct = obstruct sub + stitute = substitute
ob + ject = object sub + marine = submarine
ob + tain =obtain sub + urban = suburban
ob + serve = observe sub + traction =subtraction
ob + pose = oppose sub + pose = suppose
ob + cupy = occupy sub + plies = supplies
ob + casion = occasion sub + cessful = successful
ob + ficial = official sub + ficient = sufficient
ob + fered = offered sub + gestion = suggestion

The prefix ob means "against" or "in the way of." The prefix sub means "under," "below," or "in place of." Each of these prefixes can be spelled in different ways. The spelling depends on the roots to which the prefix is joined.

1. The prefix ob has been added to each root in the first group. How is the prefix spelled when joined to roots that begin with the letter p? _____ with the letter c? _____ with the letter f? _____

2. The prefix sub has been added to the second group of roots. How is the prefix spelled when joined to roots that begin with the letter p? _____ with the letter c? _____ with the letter f? _____ with the letter g? _____

Lesson Generalization

The letter b in the prefixes ob and sub often changes to blend more easily with the first letter of a root. When it changes to match the letters p, c, f, and g, the result is a double consonant. Remember that one of the double letters in these spelling words is a b in disguise.


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