Kohelet is a chronicle of King Solomon's life journey to understand the 'meaning of it all'. In this short klaf the phrase לִבִּי (and variants on the word for 'heart') is used some 30 times (mainly in chapters 1-2).
Is there a stylistic reason why he uses the phrase לִבִּי in a way that he seems to be referring to some entity outside or separate from himself i.e. as if it is his heart that is the object experiencing everything or that he is consulting with. Some examples:
וְנָתַתִּי אֶת-לִבִּי, לִדְרוֹשׁ וְלָתוּר בַּחָכְמָה
דִּבַּרְתִּי אֲנִי עִם-לִבִּי, לֵאמֹר--אֲנִי הִנֵּה הִגְדַּלְתִּי וְהוֹסַפְתִּי חָכְמָה
וְלִבִּי רָאָה הַרְבֵּה, חָכְמָה וָדָעַת
וָאֶתְּנָה לִבִּי לָדַעַת חָכְמָה, וְדַעַת הוֹלֵלֹת וְשִׂכְלוּת
לֹא-מָנַעְתִּי אֶת-לִבִּי מִכָּל-שִׂמְחָה, כִּי-לִבִּי שָׂמֵחַ מִכָּל-עֲמָלִי, וְזֶה-הָיָה חֶלְקִי, מִכָּל-עֲמָלִי
This can probably be attributed to 'his heart' personifying self-discovery and inner turmoil and the likes. Is there any other reason why it seems as though his 'heart' is a separate entity? Do any commentaries discuss this?