change in the sentence word order through stress (tréisiú)

The syntax in Irish is quite rigid (PSO or. VSO, see word order ). Althought, this is often skirted with the following changes inf the word order. This actually does not only happen for a special emphasis (treisiú) or reinforcement (néartú), but also to bring variety in speech/writing and is therefore common.

with the help of the copula (cleft- and pseudo-cleft construction)

The emphasis using a copular construction is the most common variety of changing the word order in Irish.
There are two basic variations, which actually - although rare - also exist in German:

the cleft construction (an abairt scoilte)
The part of the sentence to be emphasised is split off the sentence "cleft" and appears as the predicate of the copula in a copular clause. The rest of the sentence follows then as a relative clause. In German and Irish, both have a similar form.
e.g.: Is teach a thógann sé = It is a house, that he builds (instead of: Tógann sé teach = He builds a house )

the pseudo-cleft construction (an abairt bhréagscoilte)
This acts as the construction similar to e.g. "What he's building, is a house ".
In this case, the part being emphasised appears at the end of the sentence, but is represented at the beginning of the sentence with a pronoun (above e.g. "what", Irish "séard").
After the pronoun, follows a relative clause in Irish (different to the German).
e.g.: Séard a thógann sé ná teach = What he builds, is a house

In German, as opposed to Irish, cleft and pseudo-cleft constructions are a rather rare occurrance of rearranged clause elements. Much more common are freestyle rearrangements of the word order. This is not possible in Irish and therefore cleft- and pseudo-cleft constructs must take the place of that.
 

the cleft construction to emphasise the subject, object, verbal noun and other construction elements

• This is the most common form of emphasis. It can be used for all clause elements (except for verbs and subordinating clauses)
• The element to be emphasised moves to the beginning of the sentence in the form of a copular construction (most simply as is + word/phrase), which means it becomes the predicate of a copular clause.  
  The rest of the sentence follows as a direct relative clause. Whereby here, it's not always an apparent logical and understandable direct relative relationship between the antecedent and the relative clause (for example by adverbs as the antecedent).
  Moreover, the relative clause is independent and functions quasi as the subject of the new copular clause. This is why it is also called independent relative clause (an clasál coibhneasta leithleach).
• In place of is any other copula form (interrogative, negative, relative etc) is possible, depending on the situation (ní, an, nach, etc.)
• preterite forms (ba, níor, ar, nar, etc.) are to be avoided. In their place, present tense forms are used.
• The copular form is can often be omitted, but other forms of the copula cannot. Preceding indefinite nouns, it is mostly omitted.
• Preceding definite nouns, as always by the copula,  comes the corresponding pronoun é/í/iad as a subpredicate.
  If is is omitted, then one no longer needs this pronoun (e.g. Is é an fear a ... or An fear a ...)

• with adverbs and indirect objects (with a preposition), but also an indefinite direct objecten,  instead of is also is ea (comes afterwards) is used:
  (i.e.: In the copular clause, there is another shift in the form of a left shift of the predicate instead)
  e.g.: Abhaile is ea a théann an fear = Home is where the man goes.
• By subjects and definite direct objects, é/í/íad may also follow is, which is much less commonplace.
  e.g. An fear is é a fhéiceann tú = The man it is, that you see
• supplementary queries (with interrogative particle) always demonstrate a cleft construction, whereby copula and interrogative mostly fuse into one word.
  (e.g.: cé = who-is[-it]):
  e.g.: Cé a rinne é? = Who did it? (lit.: "Who-is[-it], that did it?")

If the verbal noun and object are split through the shift of the clause element, then the object is in the nominative/accusative and no londer in the genitive (2nd and 3rd example of the table)
If the object is pulled in front of the verbal noun in sentences in the progressive, then a (lenition!) takes the place instead of ag preceding the verbal noun (3rd example in the table)!
A theoretically plausable indirect relative clause like *Is scríobh a bhfuil mé an leabhar aige is not possible, ag and verbal noun are not split.

the cleft construction to emphasise the verb using the verbal noun and déan

A verb cannot be emphasised in a cleft construction like those above, because it already stands at the beginngin of a normal sentence. One can however place the verbal noun of the verb at the beginning, and following that, a relative clause with a form of the verb déan (= do) (similar as the poor German: Laufen tust du)
 

This cleft construction is basically a sentence form with déan = do as an auxilliary verb like:
Rinne tú an fear a fheiceáil = You did see the man. (lit.: "did you the man to see ").
In this form, it is used most often with rare verbs, to avoid their inflexion.

the cleft construction with comparative adjectives

This applies not only to sentences with a special emphasis af one part of the sentence, but also in other occasions where a relative clause is needed.
This form also doesn't really serve to specially emphasise the comparative.
On the practical side, the resulting construction always forms a cleft construction (is + comparative + relative clause).
This form is, of course, not to be used if the relative clause should only serve to highlight the comparative:
e.g.: an fear a bhí níos sine ná mise = the man who was older than me

the pseudo-cleft construction to emphasise the verb

An emphasis of the verb as in the above patterns (i.e. as the cleft construction) is only possible in the form of the verbal noun.
The verb, or the action clause, can also be emphasised, by placing certain expressions in front of it that point to the fact that the action is in the spotlight of interest.
Such expressions as: "Is é an chaoi" = "the way it is " or "is é an rud = the thing is", "is amhlaidh = so it is " or "is ea = it is "
This is grammatically a "pseudo-cleft construct".
 

"Is a an chaoi" requires an indirect relative clause (comp. adverbial indir. relative clause), hence the eclipsis after a or lenition after ar in the preterite (hence ar bhuail in the above example instead of a bhuail in the other examples)
"Is é an rud" can be contracted to one word: séard (Séard a bhuail tú an fear). "Is ea" becomes then "Sea"

the pseudo-cleft construction to emphasise a go/nach-subordinating clause

Such a subordinating clause can only be emphasised through the formation of a "pseudo-cleft construction", similar to the emphasis of verbs.

"Is é an rud" can be contracted to one word: Séard
Instead of "séard" one can use other expressions, e.g. rud eile = something else / what's more, etc.
e.g.: Rud eile atá speisiúil faoin teach seo ná go raibh cónaí air ann = Something else interesting about this house is that he had lived there .

Similar to the go/nach-subordinating clause, an infinitive construction may be also be emphasised by a pseudo-cleft construction:
e.g.: Séard a dúirt sé leis ná an féar a bhaint. = What he told him was is that he was to cut the grass .

the pseudo-cleft construction to emphasise the object

An object can be emphasised using a cleft construction (see above), but also with a pseudo-cleft construction. The emphasis comes about when one moves the object to the end of the sentence.
This way of shifting emphasis is also possible for subjects, but less common and most likely restricted to interrogative clauses.
 

"Is é an rud" can be contracted to one word: séard
Note the use of the conjunction ná (lit.: but): It's possibly comparable to: You've seen nothing but a horse.

the pseudo-cleft construction as an interrogative construction

Similar pseudo-cleft construction syntaxes may also be attained in (mostly rhetorical) questions.
Instead of "is é an rud (séard)" comes then words like céard, cad, cé.
Here, instead of ná often ach:
e.g.:
Céard eile a chonaic sí ansin ach capall? = What else did she see there but a horse?
Cad a dhéanfainn, mar sin, ach é a bhualadh? = What else should I have done but to hit him ?

cleft- and pseudo-cleft construction in the copular construction istelf

Cleft- and pseudo cleft constructs are formed using the copula, but also appear in various copular clauses themselves,
see here: emphasis in the copular clause.

without the help of the copula (so-called "left shift")

emphasis of the subject

If a subject is modified by an expansion (e.g. a relative clause or other adverbial construct) is becomes rather long and there fore clumsy in the normal PSO-sentence structure.
Therefore, it can move to the beginning of the sentence (i.e. shifted to the left. Hence the term left shift )
The actual main clause follows unchanged, the subject is represented there in its normal position by a reflexive pronoun, to ensure continuity of meaning.
In the German or English comparative clause such a pronoun is lacking, so below, the extra "he" is rather atypical.
e.g. (subject bold, expansion italicised):

emphasis of the object

In negative clauses, one can often shift the object to the front. It shows a particularly strong emphasis (of the negation, not the object).
It is one of the rare forms, in which one actually goes against the PSO syntax rule.
 

In clauses in the progressive:

Here, the object can also be positioned at the beginning of negative clauses, it then is in the nominative/accusative. There is then a instead of ag preceding the verbal noun.
 

emphasis of the predicate in the classificatory clause

The sentence form Dochtúir is ea é = He is a doctor is meant here
For more information, see: emphasis in the copular clause