Sometimes a pattern calls for p2togtbl (purl two together through back loop). It does this so the stitches to be knitted together will lie the right way, usually as seen from the opposite side, which is frequently the right side of the fabric.
But many people dislike working this stitch. No less revered a figure than Hansi Singh has called it "the most awkward stitch in all of knitting."
Fear not, for there is an easier way to accomplish the same effect. The answer lies in backward knitting (see previous post).
When you reach the stitches to be purled together through their back loops, do this:
1. Turn your work around so that the live yarn is on the left needle and the stitches to be worked are on the right needle.
2. Slip these two stitches to the left needle.
3. Insert tip of right needle through both these stitches, passing from right to left.
4. Catch the live yarn with the right needle, and pull a loop through both stitches, letting them slip from the needle.
5. Transfer this loop to the left needle.
6. Turn your work back to its original position and continue knitting (or purling, as the case may be).