weak verbs?

Searched for the -ed suffix in a dictionary. Got this.

-ed1
a suffix forming the past tense of weak verbs: he crossed the river.

What do they mean by weak verbs?

Weak verbs are those verbs that are not strong.

Usually strong verbs have an 'n' somewhere in the past participle. Weak verbs often have a 'd' or 't' somewhere in the past tense or past participle.

Examples:

strong -- freeze / froze / frozen, sink / sank / sunk

weak -- think / thought / thought

But why are they called weak and strong?

Here's some information:

http://en.wikipedia.org/wiki/Strong_inflection
http://en.wikipedia.org/wiki/Weak_inflection

http://en.wikipedia.org/wiki/Weak_verb

There's no real reason why they're called weak or strong, but strong verbs are the ones with a vowel change, like 'sink' and 'freeze' above, while weak ones don't. 'Think' is a strong verb actually; it has nothing to do with an 'n'.

Isn't it funny? "strengthen" is actually a 'weak' verb. Shouldn't that word be a 'strong' verb?

Turns out that I was wrong. According to Wikipedia, 'think' is a weak verb.

<<Isn't it funny? "strengthen" is actually a 'weak' verb. Shouldn't that word be a 'strong' verb? >>

"Strengthen" is weak, since the past tense is regular ("strengthened"). The "n" and "d/t" rule doesn't work too well if the verb already has one of these in the present tense.

German linguist Jacob Grimm coined the term 'weak verbs' because they need the help of a suffix to form their past tenses.

This list of irregular verbs indicates which are strong and which weak

http://en.wiktionary.org/wiki/Appendix:Irregular_verbs:English

These two explain the sound evolution of verbs like 'think'

http://en.wikipedia.org/wiki/Germanic_umlaut#Umlaut_in_Germanic_verbs
http://en.wikipedia.org/wiki/Germanic_spirant_law

The main thing that people need to remember is that weak verbs are those verbs which take a dental suffix or took a dental suffix which has been subsequently elided to form their preterite; it actually has nothing to do with whether verbs are regular or not, even though most weak verbs in English are regular (as which weak ending to use is normally predictable in English and only a small portion of those weak verbs which do not have stem changes use weak endings other than those which one would normally predict). Note that some Germanic languages have more complications with respect to weak verbs, such as where Dutch has both d-weak verbs and t-weak verbs which are not nearly as predictable as in English.