I see in the Avi Ezri of Rav Shach that he equates mashkon and eravon, and he has good reason to do so since the Gemara itself (bava metzia page 48) asks from one to the other and that implies that they are the same. However, the case of mashkon is a guarantee for a loan and eravon is a guarantee for a sale, and the Rambam does not equate them. The eravon guarantees the whole sale like R Yochanan said in Bava Metzia 48. A mashkon is for a loan or other obligations. There the mashkon guarantees just the amount parallel to its worth (as per Laws of Loans chapter 13 law 4)---------------------I see in the אבי עזרי of רב שך that he equates משכון and עירבון, and he has good reason to do so since the גמרא itself (בבא מציעא מ''ח ע''ב) asks from one to the other and that implies that they are the same. However, the case of משכון is a guarantee for a loan and עירבון is a guarantee for a sale, and the רמב''ם does not equate them. The עירבון guarantees the whole sale like ר' יוחנן said in בבא מציעא דף מ''ח. A משכון is for a loan or other obligations. There the משכון guarantees just the amount parallel to its worth (as per הלכות מלווה ולווה chapter 13 הלכה 4)--I think here is a good place to say what Rav Shach says. He says that eravon and mashkon are equal in so far as their value is weighed equal to the value of the loan or the sale, [in the approach of the Ramban]. However, he makes it clear that even so, if the mashkon or eravon is lost, they are evaluated only as according to their monetary worth [sine the law is not like Shmuel]. That is to say, that the first case is that the eravon is what causes acquisition of the sale, but not that if lost the value is that of the whole sale. It is rather like a kinyan sudar that causes a sale to be final, even though the sale might be worth millions while the handkerchief is worth two cents.------------------------I think here is a good place to say what רב שך says. He says that עירבון and משכון are equal in so far as their value is weighed equal to the value of the loan or the sale, [in the approach of the רמב''ן]. However, he makes it clear that even so, if the משכון or עירבון is lost, they are evaluated only as according to their monetary worth [since the law is not like שמואל]. That is to say, that the first case is that the עירבון is what causes acquisition of the sale, but not that if lost the value is that of the whole sale. It is rather like a קניין סודר that causes a sale to be final, even though the sale might be worth millions, while the handkerchief is worth two cents.--------------------נראה שזהו המקום המתאים לציין את דברי הרב שך. הוא קובע כי עירבון ומשכון שווים זה לזה בכך שערכם נמדד כשווי ההלוואה או המכירה (לשיטת הרמב"ן). עם זאת, הוא מבהיר כי למרות זאת, אם המשכון או העירבון אבודים, הם מוערכים אך ורק לפי שווים הכספי (שכן ההלכה אינה כדעת שמואל). כלומר, במקרה הראשון העירבון הוא הגורם להשלמת המכירה, אך אין פירוש הדבר שאם הוא אובד, ערכו נחשב כשווי המכירה כולה; הדבר דומה לקניין סודר, הגורם למכירה להיות סופית ומוחלטת, אף על פי שהמכירה יכולה להיות שווה מיליונים בעוד שהמטפחת שווה פרוטות ספורות. ------So Rav Shach equates mashkon and eravon in so far as they cause the exchange, (the loan or the sale), to be valid. But if lost, they are evaluated only according to their monetary worth. However, what makes a loan valid is not the receiving of the maskon by the lender, but rather by the receiving of money by the borrower. Also, in terms of a sale, no one thinks that to receive a partial amount by the giving of some object, that if that object is lost the whole sale goes to the buyer. That was not up for discussion in the first place.-----So רב שך equates משכון and עירבון in so far as they cause the exchange, (the loan or the sale), to be valid. But if lost, they are evaluated only according to their monetary worth. However, what makes a loan valid is not the receiving of the משכון by the lender, but rather by the receiving of money by the borrower. -----אם כן, רב שך משווה בין משכון לבין עירבון בכך ששניהם מקנים תוקף לעסקה (הלוואה או מכירה); אולם במקרה של אובדן, הם נמדדים אך ורק על פי שווים הכספי. עם זאת, הגורם המקנה תוקף להלוואה אינו קבלת המשכון על ידי המלווה, אלא קבלת הכסף על ידי הלווה