The Chinukh's presentation of the mitzvot associated with nezirut offers a reasoned account of the institution's purpose and legal components. This supports a conceptual discussion of why the Torah treats the nazirite period as a defined unit and how that may affect ambiguous declarations.
מִדִּינֵי הַמִּצְוָה. מָה שֶׁאָמְרוּ זִכְרוֹנָם לִבְרָכָה (שם לט, א) שֶׁאִם נִתְגַּלַּח הַנָּזִיר בֵּין בְּזָדוֹן בֵּין בִּשְׁגָגָה וַאֲפִלּוּ בְּאֹנֶס, הֲרֵי זֶה סוֹתֵר מִנְיָנוֹ וּמַתְחִיל לִמְנוֹת שְׁלֹשִׁים יוֹם, דְּקַיְמָא לַן (שם ה א) סְתָם נְזִירוּת שְׁלֹשִׁים יוֹם, כְּדֵי שֶׁיִּהְיֶה לוֹ פֶּרַע, וּבַמֶּה דְּבָרִים אֲמוּרִים (רמב"ם נזירות ו א) כְּשֶׁנִּתְגַּלַּח בְּרֹב רֹאשׁוֹ בֵּין בְּתַעַר בֵּין בְּמִין תַּעַר וְלֹא נִשְׁאַר כְּדֵי לָכֹף רֹאשָׁן לְעִקָּרָן, אֲבָל גִּלַּח מִעוּט שְׂעַר רֹאשׁוֹ אֵינוֹ סוֹתֵר מִנְיָנוֹ מִפְּנֵי כֵן, וּכְמוֹ כֵן אֵינוֹ סוֹתֵר מִנְיָנוֹ מִפְּנֵי שְׁתִיַּת הַיַּיִן וַאֲפִלּוּ שָׁתָה מִמֶּנּוּ יָמִים רַבִּים, אֲבָל סוֹתֵר הוּא מִנְיָנוֹ מִפְּנֵי הַטֻּמְאָה, כְּמוֹ שֶׁמְּפֹרָשׁ בַּכָּתוּב. וּמָה שֶׁאָמְרוּ זִכְרוֹנָם לִבְרָכָה גַּם כֵּן בְּעִנְיַן נְזִירוּת, דְּכָל כִּנּוּיֵי נְזִירוּת כִּנְזִירוּת, כְּלוֹמַר, מִי שֶׁהָיָה עִלֵּג אוֹ מְקוֹמוֹת שֶׁהַכֹּל עִלְּגִין וְדַרְכָּן לוֹמַר בִּמְקוֹם נָזִיר, נָזִיק אוֹ נָזִיחַ אוֹ פָּזִיחַ, וְאָמַר אֶחָד מִלְּשׁוֹנוֹת אֵלּוּ עַל עַצְמוֹ, כְּגוֹן שֶׁאָמַר אֱהֶא נָזִיק אוֹ נָזִיחַ אוֹ פָּזִיחַ הֲרֵי זֶה נָזִיר, שֶׁאֵין אוֹמְרִים בִּנְזִירוּת שֶׁיִּהְיוּ דִּבְרֵי פִּיו בְּכִוּוּן כִּלְבָבוֹ כְּמוֹ בִּשְׁבוּעָה, אֶלָּא מִכֵּיוָן שֶׁבִּלְבָבוֹ לְהִנָּזֵר וְאָמַר דְּבָרִים שֶׁיֵּשׁ לְהָבִין בָּהֶן שֶׁיְּהֵא נָזִיר, אַף עַל פִּי שֶׁהֵן מִלּוֹת שֶׁאֵין עִנְיַן הַנְּזִירוּת מוּבָן מִתּוֹכָן יָפֶה הֲרֵי זֶה נָזִיר. וְכֵן מָה שֶׁאָמְרוּ שֶׁיְּדוֹת נְזִירוּת כִּנְזִירוּת, וּמָה הֵן הַיָּדוֹת? כְּגוֹן שֶׁאָמַר אֱהֶא וְהָיָה נָזִיר עוֹבֵר לְפָנָיו הֲרֵי זֶה נָזִיר. אוֹ שֶׁאָמַר אֱהֶא נָאֶה וְתָפַס בִּשְׂעָרוֹ הֲרֵי זֶה נָזִיר וְכֵן הָאוֹמֵר הֲרֵינִי נָזִיר מִן הַחַרְצַנִּים בִּלְבַד אוֹ מִן הַתִּגְלַחַת, אוֹ מִן הַטֻּמְאָה בִּלְבַד הֲרֵי זֶה נָזִיר גָּמוּר. וְהָאוֹמֵר הֲרֵינִי נָזִיר עַל מְנָת שֶׁאֶשְׁתֶּה יַיִן אוֹ אֶטָּמֵא לְמֵתִים אוֹ אֲגַלַּח הֲרֵי זֶה נָזִיר וְאָסוּר בְּכֻלָּם, מִפְּנֵי שֶׁהִתְנָה עַל מַה שֶׁכָּתוּב בַּתּוֹרָה וּתְנָאוֹ בָּטֵל. וְנִשְׁאָלִים עַל הַנְּזִירוּת כְּדֶרֶךְ שֶׁנִּשְׁאָלִין עַל שְׁאָר הַנְּדָרִים. וְהָאָב מַדִּיר אֶת בְּנוֹ קָטָן עַד שְׁלֹשׁ עֶשְׂרֵה שָׁנָה וְיוֹם אֶחָד בְּנָזִיר, אֲבָל לֹא הָאֵם, וְדָבָר זֶה קַבָּלָה. וְהַגּוֹיִם אֵין לָהֶם נְזִירוּת, אֲבָל יֵשׁ נְזִירוּת בַּעֲבָדִים וּבְנָשִׁים. וְהַבַּעַל וְהָאָב מֵפֵר לָאִשָּׁה נֶדֶר נְזִירוּת כְּמוֹ שְׁאָר נְדָרִים, וְכֵן הָאָדוֹן אִם יִרְצֶה כּוֹפֶה לָעֶבֶד לִשְׁתּוֹת יַיִן וּלְהִטַּמֵּא [ה' נזירות פ"א].
From the laws of the commandment is that which they, may their memory be blessed, said (Nazir 39a) that if the nazirite shaves — whether volitionally or accidentally, or even under duress — behold, this interrupts his count, and he begins to count [another] thirty days; as we hold that a standard nazirite period is thirty days (Nazir 5a), so that he will have a lock. To what do these words apply? If the majority of his head was shaved with a blade or something like a blade, and there is not enough to fold their tops over to their roots from that which remains of [what was shaved]. But if he only shaved the minority of the hair on his head, he does not interrupt his count for this. And so too, he does not interrupt his count by drinking wine, even if he drank [it] for several days. But he does interrupt his number by impurity, as the verse explains. [Also among the laws is] that which they, may their memory be blessed, said that all substitutes for the term of nazirite are effective — meaning to say, if a person had a speech impediment, or lived in a place where everyone has a speech impediment, and their way is instead of saying nazir, they say nazik, nazich or pazich and he said one of these expressions about himself, such that he said, “I will be a nazik, nazich or pazich,” behold, he is a nazirite. As we do not say that the words of his mouth must be identical to [what is in] his heart, as we do for oaths. Rather, once he has [decided] in his heart to become a nazirite and he says [something by which] it can be understood that [he wants] to be a nazirite — even though these are words that themselves do not [positively identify] him as a nazirite — behold, he is a nazirite. And so [too,] that which they said that [adjunct expressions are effective]; for example, where he says, “I shall be,” as a nazirite passes before him. Or if he says, “I will be beautiful” and holds his hair, behold, he is a nazirite. And so, one who says, “I will be a nazirite from grape seeds only,” or “shaving, or impurity only,” behold, he is a complete nazirite. And one who says, “I will be a nazirite on the condition that I will drink wine,” or “become impure,” or “shave,” behold, he is a nazirite, and all [the prohibitions of a nazirite] are prohibited to him; because [in the case of] one who makes a condition which violates the laws of the Torah, the condition is cancelled. One may request [annulment] on a nazirite vow in the same way that one requests on other vows. A father may make a nazirite oath for his son up until age thirteen, but the mother may not, and this thing is a tradition. Gentiles are not subject to [becoming a] nazirite, though women and slaves are. A husband or father may annul the nazirite vow of his wife or daughter like other vows, as may a master force his slave to drink wine or become impure. (See Mishneh Torah, Laws of Naziriteship 1.)