Various explanations have been proposed, but the reason is unknown.

The reason for this is not perfectly clear, although several explanations have been proposed.

The origin of the term is not clear and several explanations have been proposed.

Because they did not show their wealth, explanations other than desire for money have been proposed.

In the early 18th century, some scholars proposed alternative explanations.

Possible alternative explanations for results of empirical research were proposed.

Some alternative explanations for the media equation have been proposed.

For these, other possible explanations have also been proposed.

Several alternative explanations for the evidence have been proposed.

Numerous explanations have been proposed for the democratic peace.