In political science, cleavage is the division of voters into voting blocs. The preliminary assumption is that voters do not come in predefined groups of pros and cons for or against a certain subject. Ballot analysis assumes that voters opt for a certain party or decide for the solution or option that comes closest to their own position. Cleavage separates the voters into advocates and adversaries on a certain issue, or voting for a certain party. If you imagine parties on a horizontal line for a certain issue, cleavage is the vertical line that divides the parties into supporters and opponents of the issue.