Planned comparisons meet the following conditions 1. all hypotheses and significance levels are specified before data is observed 2. the full F-test must be statistically significant to proceed 3. contrasts must be orthogonal 4. no more than $J-1$ tests are conducted where $J$ is the number of levels of the factor or number of groups being compared. There are at most $J-1$ orthogonal contrasts, so the fourth condition is implied by the third condition. Orthogonal contrasts help preserve the familywise Type I error rate. Orthogonal contrasts also ensure that hypothesis testing does not result in inconsistent results.