The term "one" is derived from the concept of "unity". The term is used in two senses. One of them is mikri (incidental), which is the conventional unity. While the second is in essence and enduring - this is true (absolute) unity.
Incidental unity subdivides into two divisions. In one of these the character of multitude, collectivity, and aggregation is apparent in it, such as one genus which includes many species or like one species which includes many individuals, and like one man which is comprised of many parts or one army which includes many men.
Or like we say one Hin (measure), one Rova (measure) or one liter (ex. of rice or water) which contain smaller measures, each of which is also called "one". Every one of these things we mentioned are called "one" conventionally, because the things included under the one name are alike. Every one of them may also be called "plural" since it includes many things which when separated and isolated will each be called "one". Unity in all these manners we mentioned is Mikre (incidental). Each is a unit from one perspective and plural from another aspect.
The second division of incidental unity is the unity attributed to a single individual, who though seemingly not plural and not a collection of several things, yet is essentially plural, - being composed of matter and form, essence and incident, susceptible to "creation" and "destruction", division and combination, separation and association, change and variation. (see commentaries)
Plurality must be attributed to anything for which any of these things we mentioned applies to, for they are contradictory to unity. Unity ascribed to anything essentially plural and variable in any way is undoubtedly Mikre (an incidental property). It is unity conventionally, but not in a true sense. Strive to understand this.
The abstract thought version is numerical unity, namely, the root and beginning of all numbers. It is the sign and symbol of a beginning unprecedented by any other beginning. For every true beginning is termed "One", as for example: "And there was evening and there was morning, one day" (Gen. 1:5). Instead of saying "the first day", the verse uses the term "one (day)", because the term "one" refers to any beginning unprecedented by any other beginning. When repeated, it is called "the second", and when repeated again - "the third", and so on until the number "ten", "a hundred", "a thousand", which are also units of new series, and so on to infinity.
Therefore the definition of number is that it is a sum of units. The reason I called it "abstract thought" is because the notion of number is not perceived by the physical senses. Rather, it is grasped only in thought. It is the "numbered" object alone which is perceptible to the five senses or by some of them.
The second kind of true unity exists actually. It is that which is neither plural nor susceptible to change or variation, is not described by any of the corporeal attributes, is not subject to "creation", destruction or end. Does not move or waver, does not resemble anything nor does anything resemble it, and is not associated with anything. It is from all possible perspectives - true Unity and the root of everything plural. For as we already pointed out, unity is the cause of plurality.
The true unity has neither beginning nor finiteness because anything which has a beginning or finiteness necessarily must be subject to origination and destruction. And anything subject to these is also subject to change, and change is inconsistent with Unity. Hence, it would be more than one since it had existed as one thing and then changed into a different thing, and this necessarily implies plurality.
Similarity is also an incidental property (mikre) in anything which is similar (to something else), and whatever has an incidental property is plural. But absolute unity, in its glorious essence, is not subject to any incidental properties whatsoever in any respect.
We will answer this as follows: The ascribing of true unity is intended to express the exclusion of multitude and plurality. When we describe Him as One, we mean only the negation of any multitude or plurality. But the true Unity, cannot be described by any attribute that would connote in His glorious essence any plurality, change, or variation. With this we have completed our words, regarding the true unity and the relative unity. Note it well.
אַךְ בֵּאוּר אָפְנֵי הָאֶחָד הָאֲמִתִּי וְהָאֶחָד הָעוֹבֵר,
The distinction between true (absolute) unity and conventional unity is as follows.
הוּא שֶׁהָאֶחָד שֵׁם נִגְזַר מִן הָאַחְדוּת וְהוּא נֶאֱמַר עַל שְׁנֵי עִנְיָנִים. הָאֶחָד מֵהֶם מִקְרִי וְהוּא הָעוֹבֵר וְהַשֵּׁנִי עַצְמִי קַיָּם וְהוּא הָאֲמִתִּי,
The term "one" is derived from the concept of "unity". The term is used in two senses. One of them is mikri (incidental), which is the conventional unity. While the second is in essence and enduring - this is true (absolute) unity.
וְהָאֶחָד הַמִּקְרִי גַּם כֵּן הוּא עַל שְׁנֵי עִנְיָנִים. הָאֶחָד מֵהֶם נִרְאֶה בּוֹ הָרִבּוּי וְהַכְּלָל וְהַקִּבּוּץ כַּסּוּג הָאֶחָד אֲשֶׁר הוּא כּוֹלֵל מִינִים רַבִּים וְכַמִּין הָאֶחָד הַכּוֹלֵל אִישִׁים רַבִּים וְכָאִישׁ הָא׳ הַמְחֻבָּר מֵחֲלָקִים רַבִּים וְכַצָּבָא הָאֶחָד הַכּוֹלֵל אֲנָשִׁים רַבִּים,
Incidental unity subdivides into two divisions. In one of these the character of multitude, collectivity, and aggregation is apparent in it, such as one genus which includes many species or like one species which includes many individuals, and like one man which is comprised of many parts or one army which includes many men.
וּכְאָמְרֵנוּ כּוֹר אֶחָד וְהִין א׳ וְרֹבַע א׳ וְלִיטְרָא אַחַת וְכָל א׳ מֵהֶם כּוֹלֵל דְּבָרִים רַבִּים יֵאָמֵר עַל כ״א מֵהֶם א׳. וְכָל א׳ מִמָּה שֶׁהִזְכַּרְנוּ נִקְרָא אֶחָד עַל דֶּרֶךְ הַעֲבָרָה וְהוּא מִפְּנֵי שֶׁהַדְּבָרִים הָהֵם אֲשֶׁר יְקַבֵּץ אוֹתָם הַשֵּׁם הַהוּא שָׁוִים בְּעִנְיָן א׳ וְנִקְרָא רַב מִפְּנֵי שֶׁכּוֹלֵל דְּבָרִים רַבִּים וְכַאֲשֶׁר יִתְפָּרְדוּ הַדְּבָרִים הָהֵם וְיִתְבּוֹדְדוּ יֵאָמֵר עַל כָּל אֶחָד מֵהֶם אֶחָד וְהָאֶחָד בִּכְמוֹ הָעִנְיָנִים הָאֵלֶּה אֲשֶׁר זָכַרְנוּ מִקְרֶה וְהוּא אֶחָד מִצַּד וְרַב מִצַּד.
Or like we say one Hin (measure), one Rova (measure) or one liter (ex. of rice or water) which contain smaller measures, each of which is also called "one". Every one of these things we mentioned are called "one" conventionally, because the things included under the one name are alike. Every one of them may also be called "plural" since it includes many things which when separated and isolated will each be called "one". Unity in all these manners we mentioned is Mikre (incidental). Each is a unit from one perspective and plural from another aspect.
וְהָעִנְיָן הַשֵּׁנִי מֵאֶחָד הַמִּקְרִי הוּא הָאֶחָד הַנֶּאֱמָר עַל הָאִישׁ הָא׳ לֹא מִתְרַבֶּה וְלֹא כּוֹלֵל דְּבָרִים רַבִּים כַּנִּרְאֶה מִמֶּנּוּ אַךְ הוּא רַב בְּעַצְמוֹ מִצַּד חִבּוּרוֹ מֵחֹמֶר וְצוּרָה וְעֶצֶם וּמִקְרֶה, וְהוּא מְקַבֵּל הַהֲוָיָה וְהַהֶפְסֵד וְהַחִלּוּק וְהַחִבּוּר וְהַפְּרִידָה וְהַשִּׁנּוּי וְהַחִלּוּף וְהַשִּׁתּוּף.
The second division of incidental unity is the unity attributed to a single individual, who though seemingly not plural and not a collection of several things, yet is essentially plural, - being composed of matter and form, essence and incident, susceptible to "creation" and "destruction", division and combination, separation and association, change and variation. (see commentaries)
אִם כֵּן הָרִבּוּי יַשִּׂיג הַדָּבָר הַנֶּאֱמָר עָלָיו אֶחָד מִכָּל מָה שֶׁסִּפַּרְנוּ מִפְּנֵי שֶׁהֵם כְּנֶגֶד הָאַחְדוּת. כִּי הָאֶחָד הַנֶּאֱמָר עַל הַדָּבָר אֲשֶׁר יַשִּׂיגֶנּוּ בְּעַצְמוֹ עִנְיָן מֵעִנְיְנֵי הָרִבּוּי וְהַשִּׁנּוּי הוּא מִקְרֶה מִבְּלִי סָפֵק וְהוּא אֶחָד עַל דֶּרֶךְ הַעֲבָרָה לֹא ע״ד הָאֱמֶת. שִׂים לִבְּךָ לְהָבִין:
Plurality must be attributed to anything for which any of these things we mentioned applies to, for they are contradictory to unity. Unity ascribed to anything essentially plural and variable in any way is undoubtedly Mikre (an incidental property). It is unity conventionally, but not in a true sense. Strive to understand this.
אַךְ הָאֶחָד הָאֱמֶת יֵאָמֵר גַּם כֵּן עַל שְׁנֵי פָּנִים. הָאֶחָד מֵהֶם בְּמַחְשָׁבָה וְהַשֵּׁנִי בְּפֹעַל.
True (absolute) unity is also of two kinds. The first in abstract thought and the second in actual reality.
וְהַמַּחְשָׁבָה הוּא הָאֶחָד הַמִּנְיָנִי אֲשֶׁר הוּא שֹׁרֶשׁ כָּל מִנְיָן וּתְחִלָּתוֹ וְטַעַם הָאֶחָד הַמִּנְיָנִי שֶׁהוּא אוֹת וְסִימָן לִתְחִלָּה שֶׁאֵין תְּחִלָּה לְפָנֶיהָ כִּי כָל תְּחִלָּה אֲמִתִּית תִּקָּרֵא אֶחָד כְּמוֹ שֶׁנֶּאֱמַר (בראשית א) וַיְהִי עֶרֶב וַיְהִי בֹקֶר יוֹם אֶחָד בִּמְקוֹם יוֹם רִאשׁוֹן הוֹצִיאוֹ בִּלְשׁוֹן אֶחָד מִפְּנֵי שֶׁהָאֶחָד שֵׁם לִתְחִלָּה שֶׁאֵין לְפָנֶיהָ תְּחִלָּה וּכְשֶׁהוּא שׁוֹנֶה יִקָּרֵא שֵׁנִי וּכְשֶׁהוּא מְשַׁלֵּשׁ יִקָּרֵא שְׁלִישִׁי וְכֵן עַד עֲשָׂרָה וְאַחַר כֵּן יָשׁוּב אֶל הָאֶחָד וְאַחַר כֵּן יָשׁוּב אֶל מֵאָה וְאֶל אֶלֶף אֵין תַּכְלִית לַמִּנְיָן.
The abstract thought version is numerical unity, namely, the root and beginning of all numbers. It is the sign and symbol of a beginning unprecedented by any other beginning. For every true beginning is termed "One", as for example: "And there was evening and there was morning, one day" (Gen. 1:5). Instead of saying "the first day", the verse uses the term "one (day)", because the term "one" refers to any beginning unprecedented by any other beginning. When repeated, it is called "the second", and when repeated again - "the third", and so on until the number "ten", "a hundred", "a thousand", which are also units of new series, and so on to infinity.
וע״כ הָיָה גֶּדֶר הַמִּנְיָן כְּלָל מֻרְכָּב מִן הָאֲחֵרִים וְהַטַּעַם שֶׁקְּרָאתִיו מַחְשָׁבִי מִפְּנֵי שֶׁהַמִּנְיָן אֵינוֹ נִכְנָס תַּחַת הַחוּשִׁים הַגַּשְׁמִיִּים אֲבָל יֻשַּׂג בְּמַחְשָׁבָה. אַךְ הַמָּנוּי הוּא מֻרְגָּשׁ בַּחוּשִׁים הַגַּשְׁמִיִּים הַחֲמִשָּׁה אוֹ בְּמִקְצָתָם.
Therefore the definition of number is that it is a sum of units. The reason I called it "abstract thought" is because the notion of number is not perceived by the physical senses. Rather, it is grasped only in thought. It is the "numbered" object alone which is perceptible to the five senses or by some of them.
וְהָעִנְיָן הַשֵּׁנִי אֲשֶׁר הוּא אֶחָד אֲמִתִּי נִמְצָא בְּפֹעַל. הוּא עִנְיָן אֲשֶׁר לֹא יִתְרַבֶּה וְלֹא יִשְׁתַּנֶּה וְלֹא יִתְחַלֵּף וְלֹא יְסֻפַּר בְּמִדָּה מִמִּדּוֹת הַגַּשְׁמִיִּים וְלֹא תַּשִּׂיגֵהוּ לֹא הֲוָיָה וְלֹא הֶפְסֵד וְלֹא תִּכְלָה. וְלֹא יֶעְתַּק וְלֹא יָנוּעַ וְלֹא יִדְמֶה אֶל דָּבָר וְלֹא יִדְמֶה אֵלָיו דָּבָר וְלֹא יִשְׁתַּתֵּף עִם דָּבָר. כִּי הוּא עכ״פ אֶחָד אֱמֶת וְהוּא שֹׁרֶשׁ לְכָל מִתְרַבֶּה כַּאֲשֶׁר עָבַר מִדְּבָרֵינוּ. כִּי הָאַחְדוּת עִלַּת הָרִבּוּי,
The second kind of true unity exists actually. It is that which is neither plural nor susceptible to change or variation, is not described by any of the corporeal attributes, is not subject to "creation", destruction or end. Does not move or waver, does not resemble anything nor does anything resemble it, and is not associated with anything. It is from all possible perspectives - true Unity and the root of everything plural. For as we already pointed out, unity is the cause of plurality.
וְאֵין לָאֶחָד הָאֲמִתִּי תְּחִלָּה וְלֹא תַּכְלִית. כִּי כָל מַה שֶׁיֵּשׁ לוֹ תְּחִלָּה וְתִכְלָה מִן הַדִּין שֶׁתִּכָּנֵס הַהֲוָיָה וְהַהֶפְסֵד עָלָיו וְכָל מָה שֶׁתִּכָּנֵס הַהֲוָיָה וְהַהֶפְסֵד עָלָיו מִשְׁתַּנֶּה וְהַשִּׁנּוּי כְּנֶגֶד הָאַחְדוּת א״כ יִהְיֶה יוֹתֵר מֵאֶחָד כִּי הוּא קֹדֶם הַהַתְחָלָה לְזוּלָתוֹ אַחֲרֶיהָ (זוּלַת מָה שֶׁאַחֲרֶיהָ), וְזֶה מְחַיֵּב לוֹ הָרִבּוּי,
The true unity has neither beginning nor finiteness because anything which has a beginning or finiteness necessarily must be subject to origination and destruction. And anything subject to these is also subject to change, and change is inconsistent with Unity. Hence, it would be more than one since it had existed as one thing and then changed into a different thing, and this necessarily implies plurality.
וְכֵן הִדַּמּוּת בַּמִּתְדַּמֶּה מִקְרֶה וְכָל אֲשֶׁר יַשִּׂיגֶנּוּ מִקְרֶה מִתְרַבֶּה וְהָאֶחָד הָאֱמֶת לֹא יַשִּׂיגֵהוּ שׁוּם מִקְרֶה בְּעֶצֶם כְּבוֹדוֹ בְּשׁוּם פָּנִים.
Similarity is also an incidental property (mikre) in anything which is similar (to something else), and whatever has an incidental property is plural. But absolute unity, in its glorious essence, is not subject to any incidental properties whatsoever in any respect.
וְאִם יֹאמַר אֹמֵר שֶׁהָאַחְדוּת בָּאֶחָד הָאֱמֶת מִקְרֶה,
If one will claim that the quality of "unity" is itself an incidental property in the Absolutely One.
נֹאמַר כִּי עִנְיַן הָאַחְדוּת בָּאֶחָד הָאֱמֶת הוּא הַרְחָקַת הָרִבּוּי וְהָרַב מִמֶּנּוּ וְכַאֲשֶׁר נְסַפֵּר הָאֶחָד לֹא נְסַפְּרֵהוּ כִּי אִם בְּעִנְיַן אֲפִיסַת הָרִבּוּי וְהָרַב. וְהָאֶחָד הָאֱמֶת לֹא יְסֻפַּר בְּמִדָּה שֶׁמְּחַיֶּבֶת לְעֶצֶם כְּבוֹדוֹ רִבּוּי וְלֹא שִׁנּוּי וְלֹא חִלּוּף בְּשׁוּם פָּנִים. וּבָזֶה נִשְׁלְמוּ כָּל דְּבָרֵינוּ בָּאֶחָד הָעוֹבֵר וְהָאֶחָד הָאֱמֶת וְאַתָּה דַע לָךְ:
We will answer this as follows: The ascribing of true unity is intended to express the exclusion of multitude and plurality. When we describe Him as One, we mean only the negation of any multitude or plurality. But the true Unity, cannot be described by any attribute that would connote in His glorious essence any plurality, change, or variation. With this we have completed our words, regarding the true unity and the relative unity. Note it well.