Modal Substitutes

0I have a sentence that I am trying to label parts of speech, but having some difficulty.The sentence is:02br
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01i00I am allowed to ride the roller coaster02i02br
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00I know that 'am allowed to' is a substitute for the modal verb 'may' as in:02br
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01i00I may ride the roller coaster02i02br
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00In the second example, I have 'I' as the subject, 'may' as a modal connected to the verb 'ride', and 'the roller coaster' as a noun phrase serving as a direct object of the verb.02br
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00My question is this: How do I label the parts of the substitute 'am allowed to' to make up a modal.02br
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00I have look through phrase structure rules and cannot find a rule that says modals may be phrases made up of other parts of speech.02br
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00Any Ideas?02br
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00Calcio 0-