vouch for〜
ニューヨーク・ヤンキースのAlex Rodrigueze選手が今オフに膝の手術を行うことになりました。手術をするにあたり助言したのはロサンゼルス・レイカーズのKobe Bryant選手（バスケット）でした。以下，USA. today（12/30/11付）の記事より抜粋。
LOS ANGELES (AP) – Kobe Bryant confirms he recently directed Alex Rodriguez to the German doctor who performed the treatment the Yankees' slugger had on his right knee.
"I gave him the phone number," Bryant said Thursday night before the Los Angeles Lakers hosted the New York Knicks.
Bryant opened up about the steps he has taken to heal his arthritic joints in a rare pregame interview, crediting the therapy with dramatic improvement in his own troublesome right knee and an injured left ankle in recent months.
When Rodriguez inquired about Bryant's treatment, Bryant vouched for the German doctor who developed the course of injections of plasma-rich platelets that supposedly stimulate healing in arthritis-affected areas.
Bryant says his knee is now 95 percent healthy after at least three surgeries in the last eight years. He apparently had the same treatment done in October on his ankle, which also isn't limiting him this season.
今回の表現はvouch forです。これは「〈人・事〉を保証する，請け負う」という意味を表します。実際，「〜を保証する」という意味の表現にはassureやensureなどもありますが，ではなぜvouch forが使われているのでしょうか。LDOCEで確認してみると，
vouch for:
1 to say that you firmly believe that something is true or good because of your experience or knowledge of it.
2 to say that you believe that someone will behave well and that you will be responsible for their behavior, actions etc.
記事でvouch forが用いられた経緯として，上記の赤字（because of your experience or knowledge of it，behavior，actions）あたりがポイントのようです。Sugiuch君のコメントにもありましたが，いつも語義に関心を持ち続けていようと思います。（GP）
