Editing Germanic weak verb (section)

===Causative verbs===
A significant subclass of Class I weak verbs are (deverbal) [[causative verb]]s. They are formed in a way that reflects a direct inheritance from the PIE causative class of verbs. PIE causatives were formed by adding an accented affix ''-éy-'' to the ''o''-grade of a non-derived verb.  In Proto-Germanic,  causatives are formed by adding a suffix ''-j/ij-'' (the reflex of PIE ''-éy-'') to the past-tense ablaut (mostly with the reflex of PIE ''o''-grade) of a strong verb (the reflex of PIE non-derived verbs), with [[Verner's Law]] voicing applied (the reflex of the PIE accent on the ''-éy-'' suffix):

*{{lang|gem-x-proto|*bītaną}} (I) "to bite" → {{lang|gem-x-proto|*baitijaną}} "to bridle, yoke, restrain," i.e., "to make bite down"
*{{lang|gem-x-proto|*rīsaną}} (I) "to rise" → {{lang|gem-x-proto|*raizijaną}} "to raise," i.e., "to cause to rise"
*{{lang|gem-x-proto|*beuganą}} (II) "to bend" → {{lang|gem-x-proto|*baugijaną}} "to bend (transitive)"
*{{lang|gem-x-proto|*brinnaną}} (III) "to burn" → {{lang|gem-x-proto|*brannijaną}} "to burn (transitive)"
*{{lang|gem-x-proto|*frawerþaną}} (III) "to perish" → {{lang|gem-x-proto|*frawardijaną}} "to destroy," i.e., "to cause to perish"
*{{lang|gem-x-proto|*nesaną}} (V) "to survive" → {{lang|gem-x-proto|*nazjaną}} "to save," i.e., "to cause to survive"
*{{lang|gem-x-proto|*ligjaną}} (V) "to lie down" → {{lang|gem-x-proto|*lagjaną}} "to lay," i.e., "to cause to lie down"
*{{lang|gem-x-proto|*sitjaną}} (V) "to sit" → {{lang|gem-x-proto|*satjaną}} "to set, seat," i.e., "to cause to sit"
*{{lang|gem-x-proto|*faraną}} (VI) "to travel, go"  → {{lang|gem-x-proto|*fōrijaną}} "to lead, bring," i.e., "to cause to go"
*{{lang|gem-x-proto|*faraną}} (VI) "to travel, go"  → {{lang|gem-x-proto|*farjaną}} "to carry across," i.e., "to cause to travel" (an archaic instance of the ''o''-grade ablaut used despite the differing past-tense ablaut)
*{{lang|gem-x-proto|*grētaną}} (VII) "to weep" → {{lang|gem-x-proto|*grōtijaną}} "to cause to weep"
*{{lang|gem-x-proto|*lais}} (I, preterite-present) "(s)he knows"  → {{lang|gem-x-proto|*laizijaną}} "to teach," i.e., "to cause to know"

Essentially, all verbs formed this way were conjugated as Class I weak verbs.

That method of forming causative verbs is no longer productive in the modern Germanic languages, but many relics remain. For example:
*The original strong verb ''fall fell fallen'' has a related weak verb ''fell felled felled'', which means "to cause (a tree) to fall"
*Strong ''sit sat sat'' and ''lie lay lain'' are matched with weak ''set set set'' and ''lay laid laid'', meaning "to cause something to sit" or "lie" respectively.

In some cases, phonological or semantic developments make the pairs difficult to recognise. For example:
*''Rear'' is the regular phonological development of Proto-Germanic {{lang|gem-x-proto|*raizijaną}} given in the above list, but the connection between ''rise'' and ''rear'' is no longer obvious. The word ''raise'' also ultimately defines from ''*raizijaną'', but only via borrowing from Old Norse. The connection is perhaps made more obvious by noting that ''to rear a child'' is essentially synonymous with ''to raise a child''.
*''Drench'' was originally the causative of ''drink'', but the modern meaning of "drench" ("to cause to get wet") is no longer similar to "cause to drink". 
*Similarly, German strong {{lang|de|leiden litt gelitten}} ("to suffer") has the derived weak verb {{lang|de|leiten}} ("to lead"), which makes sense when one realises that {{lang|de|leiden}} originally meant "walk, go" and came to its present meaning through the idea of "undergoing" suffering.