"When learning Greek, never use an interlinear New Testament."
Nah.
Interlinears can be some of the most useful tools when acquiring a foreign language. I used them regularly while teaching myself German, Latin, and French. I have at least 4 Greek-English New Testament interlinears in my office. I don't use them nowadays but I will always be glad I had them when I was starting out.
The ideal is to be able to read your Greek New Testament without any helps. In the meantime, halitosis is better than no breath at all (as one preacher once put it).
