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I think it's best (though others disagree) to approach punctuation as a set of minimalist notations that attempt to reflect a very limited range of speech behaviors.

In speech, the syntactic boundaries of a phrase or a clause are marked by pauses of differing duration (usually lasting only fractions of a second) and also by intonational contours. Even a microsecond pause or a subtle shift in tonality can resolve ambiguities in conversation.

Writing conventions approximate these natural expressive cues with punctuation. Punctuation reflects the internal structure of the sentence, identifying the role played by phrases and clauses. Some marks like the question mark (?) or the exclamation point (!) provide a very broad-brush clue about the main intonational contour.

Supplemental information is usually isolated from the surrounding phrases by relatively longer syntactic pauses, whereas essential information is usually delivered as a contiguous syntactic unit.

Let's consider slightly different versions of your original sentence.

My brother in Canada is an architect.

This implies that the speaker has more than one brother. The architect is the one who is in Canada. "In Canada" is a reduced restrictive clause. It is an essential piece of information to identify which brother the speaker has in mind.

The sentence would be spoken:

{My brother in Canada} is an architect.

That is, the subject-phrase would be more-or-less contiguous, a unit, with no syntactic pause separating "my brother" and "in Canada". 

My brother, who is in Canada, is an architect.

In this textual snippet of speech, the speaker is adding some extra information: My brother happens to be in Canada at the moment. There is no implication that he has more than one brother.

Now, if we leave out the commas:

My brother who is in Canada is an architect.

we are back to a full (not a reduced) restrictive clause: the speaker has more than one brother and wants to make clear that the architect is the one in Canada. The absence of commas reflects that fact that the isolating pauses that accompanied the extra information are absent in this speech, that is, the speaker is providing essential, not supplemental, information.

Supplemental information is usually isolated from the surrounding phrases by relatively longer syntactic pauses, whereas essential information is usually delivered as a contiguous syntactic unit.

In actual speech, it would typically include some extra cues:

My brother who's in CANada is an architect.

The first syllable of Canada would typically receive extra stress. But punctuation, like musical notation, takes a minimalist approach, and provides analogues for only a narrow range of speech features.

I think it's best (though others disagree) to approach punctuation as a set of minimalist notations that attempt to reflect a very limited range of speech behaviors.

In speech, the syntactic boundaries of a phrase or a clause are marked by pauses of differing duration (usually lasting only fractions of a second) and also by intonational contours. Even a microsecond pause or a subtle shift in tonality can resolve ambiguities in conversation.

Writing conventions approximate these natural expressive cues with punctuation. Punctuation reflects the internal structure of the sentence, identifying the role played by phrases and clauses. Some marks like the question mark (?) or the exclamation point (!) provide a very broad-brush clue about the main intonational contour.

Let's consider slightly different versions of your original sentence.

My brother in Canada is an architect.

This implies that the speaker has more than one brother. The architect is the one who is in Canada. "In Canada" is a reduced restrictive clause. It is an essential piece of information to identify which brother the speaker has in mind.

My brother, who is in Canada, is an architect.

In this textual snippet of speech, the speaker is adding some extra information: My brother happens to be in Canada at the moment. There is no implication that he has more than one brother.

Now, if we leave out the commas:

My brother who is in Canada is an architect.

we are back to a full (not a reduced) restrictive clause: the speaker has more than one brother and wants to make clear that the architect is the one in Canada. The absence of commas reflects that fact that the isolating pauses that accompanied the extra information are absent in this speech, that is, the speaker is providing essential, not supplemental, information.

Supplemental information is usually isolated from the surrounding phrases by relatively longer syntactic pauses, whereas essential information is usually delivered as a contiguous syntactic unit.

In actual speech, it would typically include some extra cues:

My brother who's in CANada is an architect.

The first syllable of Canada would typically receive extra stress. But punctuation, like musical notation, takes a minimalist approach, and provides analogues for only a narrow range of speech features.

I think it's best (though others disagree) to approach punctuation as a set of minimalist notations that attempt to reflect a very limited range of speech behaviors.

In speech, the syntactic boundaries of a phrase or a clause are marked by pauses of differing duration (usually lasting only fractions of a second) and also by intonational contours. Even a microsecond pause or a subtle shift in tonality can resolve ambiguities in conversation.

Writing conventions approximate these natural expressive cues with punctuation. Punctuation reflects the internal structure of the sentence, identifying the role played by phrases and clauses. Some marks like the question mark (?) or the exclamation point (!) provide a very broad-brush clue about the main intonational contour.

Supplemental information is usually isolated from the surrounding phrases by relatively longer syntactic pauses, whereas essential information is usually delivered as a contiguous syntactic unit.

Let's consider slightly different versions of your original sentence.

My brother in Canada is an architect.

This implies that the speaker has more than one brother. The architect is the one who is in Canada. "In Canada" is a reduced restrictive clause. It is an essential piece of information to identify which brother the speaker has in mind.

The sentence would be spoken:

{My brother in Canada} is an architect.

That is, the subject-phrase would be more-or-less contiguous, a unit, with no syntactic pause separating "my brother" and "in Canada". 

My brother, who is in Canada, is an architect.

In this textual snippet of speech, the speaker is adding some extra information: My brother happens to be in Canada at the moment. There is no implication that he has more than one brother.

Now, if we leave out the commas:

My brother who is in Canada is an architect.

we are back to a full (not a reduced) restrictive clause: the speaker has more than one brother and wants to make clear that the architect is the one in Canada. The absence of commas reflects that fact that the isolating pauses that accompanied the extra information are absent in this speech, that is, the speaker is providing essential, not supplemental, information.

In actual speech, it would typically include some extra cues:

My brother who's in CANada is an architect.

The first syllable of Canada would typically receive extra stress. But punctuation, like musical notation, takes a minimalist approach, and provides analogues for only a narrow range of speech features.

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I think it's best (though others disagree) to approach punctuation as a set of minimalist notations that attempt to reflect a very limited range of speech behaviors.

In speech, the syntactic boundaries of a phrase or a clause are marked by pauses of differing duration (usually lasting only fractions of a second) and also by intonational contours. Even a microsecond pause or a subtle shift in tonality can resolve ambiguities in conversation.

Writing conventions approximate these natural expressive cues with punctuation. Punctuation reflects the internal structure of the sentence, identifying the role played by phrases and clauses. Some marks like the question mark (?) or the exclamation point (!) provide a very broad-brush clue about the main intonational contour.

Let's consider slightly different versions of your original sentence.

My brother in Canada is an architect.

This implies that the speaker has more than one brother. The architect is the one who is in Canada. "In Canada" is a reduced restrictive clause. It is an essential piece of information to identify which brother the speaker has in mind.

My brother, who is in Canada, is an architect.

In this textual snippet of speech, the speaker is adding some extra information: My brother happens to be in Canada at the moment. There is no implication that he has more than one brother.

Now, if we leave out the commas:

My brother who is in Canada is an architect.

we are back to a full (not a reduced) restrictive clause: the speaker has more than one brother and wants to make clear that the architect is the one in Canada. The absence of commas reflects that fact that the isolating pauses that accompanied the extra information are absent in this speech, that is, the speaker is providing essential, not supplemental, information.

Supplemental information is usually isolated from the surrounding phrases by relatively longer syntactic pauses, whereas essential information is usually delivered as a contiguous syntactic unit.

In actual speech, it would typically include some extra cues:

My brother who's in CANada is an architect.

The first syllable of Canada would typically receive extra stress. But punctuation, like musical notation, takes a minimalist approach, and provides analogues for only a narrow range of speech features.