1. RASHI METHOD: REFERENCES BRIEF EXPLANATION: Commentary on a verse is provided thru a cross-reference to another verse. The cross references can either provide (1a) further details, (1b) confirm citations, or (1c) clarify word meaning. This examples applies to Rashis Nu19-15a URL Reference: (c) http://www.Rashiyomi.com/w33n25.htm; Brief Summary: ALL OPEN UNSEALED VESSELS - Rashi: CLAY VESSELS, because clay vessels only receive ritual impurity from air space contact inside (Lv11-32:33)

Verse Nu19-15a, discussing which objects receive ritual impurity from a dead corpse, states ...And every open utensil, which is not sealed, is unclean. Rashi clarifies the underlined words open utensil which is not sealed by referencing verse(s) Nu11-32:33, discussing how dead animals cause ritual impurity to utensils which states ###### And every earthen utensil, in which any of them falls in it, whatever is inside shall be unclean; and you shall break it. Hence the Rashi comment: Other utensils receive ritual impurity by touch (falling). Earthenware vessels receive ritual impurity by corpse contact with their inside air-space. Hence when the verse speaks about an open utensil which is not sealed as receiving ritual impurity it must be referring to an eartherware vessel, since this is the only vessel where sealing would protect it.

Text of Target verse Nu19-15a	Text of Reference Verse Nu11-32:33
...And every open utensil, which is not sealed, is unclean.	###### And every earthen utensil, in which any of them falls in it, whatever is inside it shall be unclean; and you shall break it.
Rashi comments: Other utensils receive ritual impurity by touch (falling). Earthenware vessels receive ritual impurity by corpse contact with their inside air-space. Hence when the verse speaks about an open utensil which is not sealed as receiving ritual impurity it must be referring to an eartherware vessel, since this is the only vessel where sealing would protect it.

Advanced Rashi: A careful examination of the verses Lv11-32:33 requires the alignment method: Lv11-32 speaks about a dead animal corpse falling on a utensil; here touch results in ritual impurity. By contrast verse Lv11-33 speaking about an eartheware vessel describes the transmission of ritual impurity as achieved through contact with its inside that is, its air space. Rashi then concludes that vessel seals would only be relevant to an earthenware vessel.