Morphosyntactic alignment is about how the different core arguments of a verb are grouped into cases (wether these are explicitly marked or not is irrelevant. Well... most of the time, anyways*). Let's take a look at the different kinds of core arguments:
S: Subject (sometimes Experiencer) of an intransitive sentence
A: Agent of a transitive sentence
P: Patient of a monotransitive sentence
R: Receiver of a ditransitive sentence
T: Theme of a ditransitive sentence
Intransitive: He (S) sleeps
Monotransitive: He (A) hits her (P)
Ditransitive: He (A) gives her (R) a book (T)
Let's look at the grouping of S, A, and P first.
- Accusative languages group S and A into the nominative. P becomes the accusative. f.e. English
Ergative languages group S and P into the absolutive. A becomes the ergative. f.e. Basque
Tripartite languages assign a different case to each: S is the intransitive, A the ergative and P the accusative. f.e. Wangkumara
Active languages (sometimes called split-ergative) group S with P or with A, depending on an external factor. This can be wether S is in control or not, wether the verb represents a state or an action, ... or it can be completely arbitrary. The two resulting cases are commonly called agentive and patientive, but also ergative and accusative respectively. f.e. Georgian, sometimes
Some other languages exhibit even weirder alignments, like an animacy hierarchy (aka direct/inverse system). I'm not sure about this, but I think I even read about a language which groups A with P and marks S differently. Which is pretty damn crazy.
Now let's look at the grouping of P, R and T. This part of alignment usually receives less attention... a pity, really.
- Dative languages (or direct/indirect-object-languages) group P with T. R becomes the dative. f.e. English
Dechticaetiative languages (or primary/secondary-object-languages) group P with R. T becomes the dechticaetiative. f.e. Yoruba
There are also languages that group P, R and T in a single case, and rely completely on context in ditransitive sentences to make out which is which.
Some examples:
English is accusative-dative.
Basque is ergative-dative.
Yoruba is accusative-dechticaetiative.
So, what's your language's morphosyntactic alignment?** You are encouraged to draw a diagram and provide examples. Conlangs are welcomed. ;)
*: Some languages show different alignments morphologically and syntactically.
**: I realise that this question is perhaps a bit oversimplified: some languages show different alignments depending on other factors like verb tense, 1st, 2nd or 3rd person, ... in that case, feel free to elaborate smile
