A purchaser who is injured by a product has a cause of action by demonstrating all of the following are true except one. The exception is:

To determine the exception among the given options, we need to analyze each statement and identify the one that does not belong. Let's go through each choice one by one:

1) The product had a defect: This is a crucial element of a cause of action for an injured purchaser. If the product had a defect that caused harm to the purchaser, they would have a valid claim.

2) The injury was caused by the defect: Another vital aspect of a cause of action is proving that the injury was a direct result of the product's defect. If the defect led to the injury, the purchaser would have a valid claim.

3) The purchaser was aware of the defect but still chose to use the product: This is an important exception to a cause of action. If the purchaser was fully aware of the defect in the product but still decided to use it, their knowledge of the defect could potentially negate their ability to bring a successful claim.

4) The purchaser was using the product in an intended or foreseeable manner: This is an essential consideration for establishing a cause of action. If the purchaser was using the product as intended or in a reasonably foreseeable manner, their claim would be strengthened.

Based on the above analysis, it appears that the exception among the given choices is:

3) The purchaser was aware of the defect but still chose to use the product.

If the purchaser had knowledge of the defect but still decided to utilize the product, it could potentially weaken their cause of action.