Easy Croatian: A3 Verbs
I will introduce more types of verbs. They will all cause problems to you.
Weird 0-verbs in Present
There are 0-verbs having 1st pers. sg. on -em that have one sound in 1st pers. sg. — 2nd pers. pl. root, and a different one in the 3rd pers. pl. The difference is always -čem, -češ... in all forms except in the 3rd pers. pl, where -ku appears.
This k is then retained in the past part., and the infinitive ends on -ći instead of -ti, and the k disappears there! Examples are pečem "bake" and vučem "pull":
1st sg. peč--em vuč--em · · · 2nd pl. peč--ete vuč--ete 3rd pl. pek--u vuk--u past m pek--äo vuk--äo past f pek--la vuk--la inf. pe--ći vu--ći
Sometimes you can hear: pečeju instead of peku. It's really so in some dialects, but most people consider them mistakes children make.
Since such behavior cannot be predicted from the present form, I will list the 3rd pers. pl. in parentheses () if it shows such a shift, and all other forms, since they are regular but exceptional; e.g.:
pečem (peku), pekäo, pekla, peći "bake"
Weird 0-verbs in Past/Infinitive
There are also issues with 0-verbs in past (and of course infinitive, since it's derived from the past part.).
The first problem is that there are some verbs that change their root from present to past. It happens only for a limited number of 0-verbs; three examples are perem, prao "wash"; zovem, zvao "call" and uzmem, uzeo "take" (perf.).
The second problem also occurs in this class. There are some verbs that have roots ending, unfortunately, on -d or -t. Due to some guys having problems with pronunciation 2000 years ago, those sounds are dropped in the past. Again, two verbs will serve as examples: jëdem "eat", and pletem "knit"; the table summarizes both problems:
1st sg. per--em zov--em jëd--em plet--em 3rd pl. per--u zov--u jëd--u plet--u past m pra--o zva--o jë--o ple--o past f pra--la zva--la jë--la ple--la inf. pra--ti zva--ti jës--ti ples--ti
As you can see, infinitives for such verbs are derived from past part. f, except for an additional -s- before -ti that appears only when present root ends on a -d or -t.
All common 0-verbs with root change and other difficulties are listed in the Summary of Verb Forms.
Strange j/v Verbs
This class has two main subpatterns, where -uj- of the present changes to -ova- or -iva- in the past. However, there are three more subpatterns, shown with verbs dajem "give", pljujem "spit" (I cannot think of a better example), kraljujem "rule as a king", compared against two already presented:
1st sg. d-aj-em plj-uj-em kralj-uj-em kup-uj-em oček-uj-em 3rd pl. d-aj-u plj-uj-u kralj-uj-u kup-uj-u oček-uj-u past m d-ava-o plj-uva-o kralj-eva-o kup-ova-o oček-iva-o past f d-ava-la plj-uva-la kralj-eva-la kup-ova-la oček-iva-la inf. d-ava-ti plj-uva-ti kralj-eva-ti kup-ova-ti oček-iva-ti
As you can see, the infinitive completely follows the infinitive rule. In reality, there are only a handful of verbs similar to kraljujem, kraljevao and so on. The vast majority of j/v-verbs are like očekujem or kupujem.
Now, the last issue: some verbs use one present class and a completely different past class! The best way is just to remember the present and the past in "weird" verb classes, since there are rules, but they are quite complicated. Therefore, you can regard them "irregular" if it makes life easier for you, but really they are not.
Let's review the mixed classes. I have already shown the i/a-verbs (e.g. držim, držao).
Next, there are i/jë-verbs; they follow the pattern:
volim, volio, voljëla "love, like"
It's interesting that in speech of some people verbs from this class are moved to i-verbs (it's really similar): you will sometimes hear žel-i-la and similar (non-standard) forms.
Another mixed class is n/0. The suffix -n- is somehow lost in the past part. Some verbs in that not really big class have -d or -t that behave as 0-verbs:
1st sg. sta-n-em pad-n-em sret-n-em leg-n-em puk-n-em 3rd pl. sta-n-u pad-n-u sret-n-u leg-n-u puk-n-u past m sta--o pa--o sre--o leg--äo puk--äo past f sta--la pa--la sre--la leg--la puk--la inf. sta--ti pas--ti sres--ti le--ći pu--ći
Roots ending on g have the same effect on the infinitive as k: it will have -ći and not ti (g is lost then). The rule for infinitives is the same as for 0-verbs since it's the only the past form that matters for the infinitive.
We can summarize exceptions for forming infinitives:
Making infinitives for 0- and n/0-verbs
if the past root of a verb ends on -k or -g,
then the infinitive ends on -ći and the -k or -g is lost.
e.g. past part. pek--äo m, pek--la f → inf. pe--ći
past part. leg--äo m, leg--la f → inf. le--ći
if the present root of a verb ends on -d or -t,
(that d or t is dropped when forming the past part.)
then in the infinitive, d or t are converted to s
e.g. pres. plet--em past part. ple--la f → inf. ples--ti
pres. jed--em past part. je--la f → inf. jes--ti
There's another way to remember the rule for infinitives (if you decide to remember the rule, and not infinitives):
past f -la - dla
tla -bla -kla
inf. -ti -sti -psti -ći
Infinitive vs. Present Tense
One final remark: in dictionaries, verbs are usually listed in their infinitive form, and that's how they are traditionally learned. The problem is that it's not trivial to get the present form for some verbs, since some sounds from present (k, g, d, t) are not visible in the infinitive! These two subtypes of verbs having exceptional infinitives are then often called "ći" verbs and "sti" verbs and are considered "irregular". However, you can see they are complicated, but quite regular if you learn their present instead of infinitive!
Updated 2014-05-15 (v. 0.4)